Leucine zipper motif extends

Molecular cloning of TOPAP: a topographically graded protein in the developing chick visual system

Topographically graded molecules representing position-specific differences among otherwise similar cells are thought to play a role in the patterning of the developing nervous system. In the embryonic chick visual system, a 40 kDa protein, TOPAP, is expressed in a posterior > anterior gradient in the retina and in an inverted anterior > posterior gradient in the optic tectum, the major retinal projection area. Here we report the isolation and nucleotide sequencing of a complementary DNA clone encoding the chick TOPAP protein and demonstrate that the mRNA encoding this coiled-coil integral membrane protein is topographically graded within the retina and is present in a variety of chick tissues.

Molecular cloning of a gene expressed during early embryonic development in Onchocerca volvulus

Little attention has been paid to the reproductive biology of filarial nematode parasites as a possible target for immunological or chemotherapeutic intervention. An interruption of the reproductive process would, in addition to breaking the cycle of transmission, reduce the morbidity associated with certain filarial infections. As part of our efforts to define molecules that have important functions during filarial embryogenesis, antibodies against embryo-associated proteins were used to identify a 6308-bp cDNA sequence (ovt1) from an Onchocerca volvulus cDNA expression library. The ovt1 cDNA contained an open reading frame that coded for 2022 amino acids. The deduced amino acid sequence was highly hydrophilic, alpha-helical in nature and included two leucine zipper domains. OVT1 also contained a single Arg-Gly-Asp (RGD) site. The results of Southern blot analyses demonstrated that an ovt1-like gene occurs in a number of different species of filarial nematodes. In situ hybridization experiments to identify tissues that contain ovt1 transcripts showed that ovt1 was transcribed at high levels in the late morula/early blastocyst stage of embryonic development. Transcripts for ovt1 were also detected in O. volvulus larvae and in the hypodermal cells of adult parasites. Two fragments of ovt1 were expressed as fusion proteins and the fusion proteins were used to produce antibodies in rabbits. Both antibodies recognized a native protein with an apparent molecular mass of 230 kDa in extracts from gravid female O. volvulus. In addition, the antibodies reacted with a restricted number of lower-molecular mass bands which may represent the products of post-transcriptional or post-translational processing. The predicted coiled-coil structure and the sites of transcription suggest that OVT1 may be a component of the extracellular matrix.

Determinants of human immunodeficiency virus type 1 envelope glycoprotein oligomeric structure

Oligomerization of the human immunodeficiency virus type 1 envelope (env) glycoproteins is mediated by the ectodomain of the transmembrane glycoprotein gp41. We report that deletion of gp41 residues 550 to 561 resulted in gp41 sedimenting as a monomer in sucrose gradients, while the gp160 precursor sedimented as a mixture of monomers and oligomers. Deletion of the nearby residues 571 to 582 did not affect the oligomeric structure of gp41 or gp160, but deletion of both sequences resulted in monomeric gp41 and predominantly monomeric gp160. Deletion of residues 655 to 665, adjacent to the membrane-spanning sequence, partially dissociated the gp41 oligomer while not affecting the gp160 oligomeric structure. In contrast, deletion of residues 510 to 518 from the fusogenic hydrophobic N terminus of gp41 did not affect the env glycoprotein oligomeric structure. Even though the mutant gp160 and gp120 molecules were competent to bind CD4, the mutations impaired fusion function, gp41-gp120 association, and gp160 processing. Furthermore, deletion of residues 550 to 561 or 550 to 561 plus 571 to 582 modified the antigenic properties of the proximal residues 586 to 588 and the distal residues 634 to 664. Our results indicate that residues 550 to 561 are essential for maintaining the gp41 oligomeric structure but that this sequence and additional sequences contribute to the maintenance of gp160 oligomers. Residues 550 to 561 map to the N terminus of a putative amphipathic alpha-helix (residues 550 to 582), whereas residues 571 to 582 map to the C terminus of this sequence.

A leucine motif in the amino acid sequence of subunit 9 of the mitochondrial ATPase, and other hydrophobic membrane proteins, that is highly conserved by editing

Subunit 9 of the mitochondrial ATPase, but also other hydrophobic mitochondrially encoded proteins, contains a high frequency of the leucine motif, -Leu-X9-Leu-, which is highly conserved through RNA editing. The leucine motif may provide specific recognition sites between membrane-spanning domains of the F0-ATPase and between other hydrophobic subunits during the assembly of multienzyme complexes in the inner mitochondrial membrane.

Measles virus fusion: role of the cysteine-rich region of the fusion glycoprotein

Measles virus (MV) fusion requires the participation of both the fusion (F) and hemagglutinin (H) glycoproteins. The canine distemper virus fusion protein (CDVF) cannot substitute for the measles virus fusion protein (MVF) in this process. Introduction of restriction enzyme sites into the cDNAs of CDVF and MVF by site-directed mutagenesis facilitated the production of chimeric F proteins which were tested for their capacity to give fusion when coexpressed with MVH. Fusion resulted when the amino-terminal half of the MVF cysteine-rich region was transferred to CDVF.

Cloning, sequencing, and expression of a fibronectin/fibrinogen-binding protein from group A streptococci

Lipoteichoic acid and several streptococcal proteins have been reported to bind fibronectin (Fn) or fibrinogen (Fgn), which may serve as host receptors. We searched for such proteins by screening a library of genes from M type 5 group A streptococci cloned into Escherichia coli. Lysates of clones were probed with biotinylated Fn and biotinylated Fgn. One clone expressed a 54-kDa protein that reacted with Fn and Fgn. The protein, termed FBP54, was purified and used to immunize rabbits. Anti-FBP54 serum reacted with purified, recombinant FBP54 and with a protein of similar electrophoretic mobility in extracts of M type 5, 6, and 24 streptococci. Anti-FBP54 serum also reacted with 5 of 15 strains of intact, live streptococci, suggesting that FBP54 may be a surface antigen. Southern blot analysis confirmed that the gene is found in group A streptococci but not in Staphylococcus aureus or E. coli. The cloned gene was sequenced and contained an open reading frame encoding a protein with a calculated molecular weight of 54,186. Partial amino acid sequencing of purified FBP54 confirmed that this open reading frame encoded the protein. As determined by utilizing fusion proteins containing truncated forms of FBP54, the primary Fn/Fgn-binding domain appears to be contained in residues 1 to 89. These data suggest that FBP54 may be a surface protein of streptococci that reacts with both Fn and Fgn and therefore may participate in the adhesion of group A streptococci to host cells.

Leucine-zipper dimerization motif encoded by the AF17 gene fused to ALL-1 (MLL) in acute leukemia

Chromosome region 11q23 is involved in reciprocal chromosome translocations associated with human acute leukemias. These aberrations fuse the ALL-1 gene located at 11q23 to a series of partner genes positioned on a variety of human chromosomes. The fused genes encode chimeric proteins. Here we report the cloning and characterization of the ALL-1 partner at 17q21, the AF17 gene. The AF17 gene encodes a protein of 1093 amino acids, containing a leucine-zipper dimerization motif located 3' of the fusion point and a cysteine-rich domain at the N terminus. The latter can be arranged in three zinc fingers and shows homology to a domain within the protein Br140 (peregrin). AF17 contains stretches of amino acids previously associated with domains involved in transcriptional repression or activation. Based on features of AF17 and of the proteins encoded by the other partner genes analyzed and in conjunction with other recent studies, we propose a model in which ALL-1 rearrangements result in loss of function of the gene. In this model, the partner polypeptide plays an accessory role either by repressing activity of the truncated ALL-1 protein or by blocking the function of the normal protein presumably present in the leukemic cells.

Assignment of disulfide bridges in the fusion glycoprotein of Sendai virus

The mature fusion (F) glycoprotein of the paramyxovirus family consists of two disulfide-linked subunits, the N-terminal F2 and the C-terminal F1 subunits, and contains 10 cysteine residues which are highly conserved at specific positions. The high level of conservation strongly suggests that they are indeed disulfide linked and play important roles in the folding and functioning of the molecule. However, it has not even been clarified which cysteine residues link the F2 and F1 subunits. This report describes our assignment of the disulfide bridges in purified Sendai virus F glycoprotein by fragmentation of the polypeptide and isolation of cystine-containing peptides and determination of their N-terminal sequences. The data demonstrate that all of the 10 cysteine residues participate in disulfide bridges and that Cys-70, the only cysteine in F2, and Cys-199, the most upstream cysteine in F1, form the interchain bond. Of the remaining eight cysteine residues clustered near the transmembrane domain of F1, the specific bridges identified are Cys-338 to Cys-347 and Cys-362 to Cys-370. Although no exact pairings between the subsequent four residues were defined, it seems likely that the most downstream, Cys-424, is linked to Cys-394, Cys-399, or Cys-401. Thus, we conclude that the cysteine-rich domain indeed contributes to the formation of a bunched structure containing at least two tandem cystine loops.

Multigene families in African swine fever virus: family 505

Sequencing of restriction fragment EcoRI A-SalI C of African swine fever virus has revealed the existence of a multigene family, designated family 505 because of the average number of amino acids in the proteins, composed of seven homologous and tandemly arranged genes. All the genes of family 505 are expressed during infection. Primer extension analysis showed that transcription is initiated a short distance (3 to 62 nucleotides) from the start codon of the corresponding open reading frame. The proteins of family 505 showed similarity to those of family 360 from African swine fever virus. In particular, a striking conservation of three regions at the amino terminus of the polypeptides was observed.

Novel genes expressed differentially in ascidians with alternate modes of development

We have used a subtractive procedure to isolate cDNA clones encoding genes expressed differentially in ascidian species with alternate modes of development. The ascidians used in this study were Molgula occulta, which develops a tailed (urodele) larva, and Molgula occulta, which develops a tailless (anural) larva. Two of the identified clones, Uro-2 and Uro-11, are described. Southern blots show that the Uro-2 and Uro-11 genes are present in both species, but the corresponding mRNAs are expressed preferentially in the urodele species. In situ hybridization showed that Uro-2 and Uro-11 transcripts accumulate in small oocytes during oogenesis. The maternal Uro-2 and Uro-11 transcripts were distributed throughout the oocyte cytoplasm. Transcript concentrations declined during vitellogenesis, but mature eggs still contain detectable levels of Uro-2 and Uro-11 mRNA. After fertilization, the maternal Uro-2 and Uro-11 transcripts were localized in the ectoplasm of uncleaved zygotes and mostly entered the ectoderm cells during cleavage. The Uro-2 gene appears to produce only maternal transcripts. In contrast, the Uro-11 gene may also produce zygotic transcripts, which accumulate between gastrulation and neurulation in posterior epidermis, neural and tail muscle cells. Zygotic expression of the Uro-11 gene was not detected in embryos of the anural species. The deduced amino acid sequences of the Uro-2 and Uro-11 cDNAs suggest that they encode novel basic proteins with distinctive structural features. The predicted Uro-2 protein contain, a leucine zipper motif, suggesting that it may dimerize with another protein. The predicted Uro-11 protein contains a nuclear localization signal, a region with similarity to part of the DNA-binding motif in the bacterial histone-like HU and IHF proteins, 12 repeats of the proposed DNA-binding motif S(T)PXX, and a potential zinc finger of the C6 or C6H2 class, suggesting that it may be a DNA-binding protein. The Uro-2 and Uro-11 proteins are candidates for regulatory factors involved in the evolutionary transition from urodele to anural development.

A novel 77-residue peptide from porcine brain contains a leucine-zipper motif and is recognized by an antiserum to delta-sleep-inducing peptide

In 1977 a nonapeptide, called delta-sleep-inducing peptide (DSIP) was characterized in rabbit cerebral venous blood plasma during thalamic stimulation to induce sleep. Evidence for the existence of DSIP in the central nervous system and in numerous peripheral organs of various mammalian species has been obtained using immunochemical techniques. Later findings have revealed the existence of large forms of DSIP-like immunoreactivity. We decided to investigate the molecular identity of such large forms of DSIP-like immunoreactivity by direct isolation. We have purified and characterized using amino acid analysis, sequencing, mass spectrometry and radioimmunoassay a 77-residue peptide, denoted DIP (DSIP-immunoreactive peptide), from an acid extract of porcine brain. DIP is recognized by an antiserum raised against synthetic rabbit DSIP. The amino acid sequence of DIP, however, is not related to that of DSIP, but it contains a putative leucine-zipper motif, a proline/glutamic-acid-rich domain, three potential phosphorylation sites and exhibits an acetylated N-terminus. The N-terminal but not the C-terminal part of the newly isolated peptide shares clear homology with the sequence of a protein induced by transforming growth factor beta 1 and other growth factors in mouse osteoblastic cells. DIP is also structurally similar to a baculoviral protein p10. The function of DIP remains unclear but its involvement in transcriptional regulation is probable.

Molecular characterization of two human autoantigens: unique cDNAs encoding 95- and 160-kD proteins of a putative family in the Golgi complex

Serum autoantibodies from a patient with autoantibodies directed against the Golgi complex were used to screen clones from a HepG2 lambda Zap cDNA library. Three related clones, designated SY2, SY10, and SY11, encoding two distinct polypeptides were purified for further analysis. Antibodies affinity purified by adsorption to the lambda Zap-cloned recombinant proteins and antibodies from NZW rabbits immunized with purified recombinant proteins reproduced Golgi staining and bound two different proteins, 95 and 160 kD, from whole cell extracts. The SY11 protein was provisionally named golgin-95 and the SY2/SY10 protein was named golgin-160. The deduced amino acid sequence of the cDNA clone of SY2 and SY11 represented 58.7- and 70-kD proteins of 568 and 620 amino acids. The in vitro translation products of SY2 and SY11 cDNAs migrated in SDS-PAGE at 65 and 95 kD, respectively. The in vitro translated proteins were immunoprecipitated by human anti-Golgi serum or immune rabbit serum, but not by normal human serum or preimmune rabbit serum. Features of the cDNA suggested that SY11 was a full-length clone encoding golgin-95 but SY2 and SY10 together encoded a partial sequence of golgin-160. Analysis of the SY11 recombinant protein identified a leucine zipper spanning positions 419-455, a glutamic acid-rich tract spanning positions 322-333, and a proline-rich tract spanning positions 67-73. A search of the SwissProt data bank indicated sequence similarity of SY11 to human restin, the heavy chain of kinesin, and the heavy chain of myosin. SY2 shared sequence similarity with the heavy chain of myosin, the USO1 transport protein from yeast, and the 150-kD cytoplasmic dynein-associated polypeptide. Sequence analysis demonstrated that golgin-95 and golgin-160 share 43% sequence similarity and, therefore, may be functionally related proteins.

Mutational analysis of the leucine zipper-like motif of the human immunodeficiency virus type 1 envelope transmembrane glycoprotein

The N-terminal region of the envelope (env) transmembrane protein of human immunodeficiency virus type 1 (HIV-1) has a leucine zipper-like motif. This highly conserved zipper motif, which consists of a heptad repeat of leucine or isoleucine residues, has been suggested to play a role in HIV-1 env glycoprotein oligomerization. This hypothesis was tested by replacing the highly conserved leucine or isoleucine residues in the zipper motif with a strong alpha-helix breaker, proline. We report here that such substitutions did not abolish the ability of env protein to form oligomers, indicating that this highly conserved zipper motif does not have a crucial role in env protein oligomerization. However, the mutant viruses all showed impaired infectivity, suggesting that this conserved zipper motif can have an important role in the virus life cycle.

Identification of an amino acid that defines the fusogenicity of mumps virus

Recombinant cDNA clones representing the fusion (F) and hemagglutinin-neuraminidase (HN) proteins of two mumps virus strains different in fusogenicity were constructed. Upon transfection of COS7 cells, extensive cell fusion was observed only when cells expressed the F protein of the fusing strain together with the HN protein derived from either strain. Mutational analyses further showed that the amino acid at position 195 of the F protein plays a critical role in determining the extent of cell fusion induced by mumps virus, since replacement of Ser-195 by Tyr significantly reduced the fusion inducibility of otherwise fusion-competent F protein.

The 87K postsynaptic membrane protein from Torpedo is a protein-tyrosine kinase substrate homologous to dystrophin

Postsynaptic peripheral membrane proteins at the neuromuscular junction have been proposed to participate in the immobilization of the nicotinic acetylcholine receptor at the synapse. An 87 kd cytoplasmic peripheral membrane protein has been demonstrated to colocalize with the nicotinic acetylcholine receptor in the Torpedo electric organ and at the mammalian neuromuscular junction. We have cloned the cDNA encoding the 87K protein from Torpedo electric organ, and the predicted protein sequence is homologous to the C-terminal domains of dystrophin, the protein product of the Duchenne muscular dystrophy gene. The 87K protein displays a restricted pattern of expression detected only in electric organ, brain, and skeletal muscle. Analysis of the in vitro and in vivo phosphorylation of the 87K protein indicates that it is multiply phosphorylated on serine, threonine, and tyrosine residues. The 87K protein is in a complex with other proteins associated with the postsynaptic membrane, including dystrophin and a 58 kd protein. These results suggest that the 87K protein is involved in the formation and stability of synapses and is regulated by protein phosphorylation.

A Drosophila photoreceptor cell-specific protein, calphotin, binds calcium and contains a leucine zipper

The calphotin protein, encoded by the calphotin (cap) gene, is expressed in the soma and axons of all Drosophila photoreceptor cells. It is expressed early in photo-receptor cell development, at the time when cell-type decisions are being made. Expression of calphotin is not altered by the glass mutation, which blocks photoreceptor cell development. The calphotin protein binds calcium and contains a long C-terminal leucine zipper. Potential implications of these properties are discussed.

Mutations in the leucine zipper of the human immunodeficiency virus type 1 transmembrane glycoprotein affect fusion and infectivity

Many retroviruses, including the human and simian immunodeficiency viruses, contain a leucine zipper-like repeat in a highly conserved region of the external domain of the transmembrane (TM) glycoprotein. This region has been postulated to play a role in stabilizing the oligomeric form of these molecules. To determine what role this region might play in envelope structure and function, several mutations were engineered into the middle isoleucine of the leucine zipper-like repeat of the human immunodeficiency virus type 1 (HIV-1) TM protein. A phenotypic analysis of these mutants demonstrated that conservative mutations (Ile to Val or Leu) did not block the ability of the viral glycoprotein to mediate cell-cell fusion or affect virus infectivity. In contrast, each of the other mutations, except for the Ile-to-Ala change, completely inhibited the ability of the glycoprotein to fuse HeLa-T4 cells and of mutant virions to infect H9 cells. The alanine mutation produced an intermediate phenotype in which both cell fusion and infectivity were significantly reduced. Thus, the biological activity of the glycoprotein titrates with the hydrophobicity of the residue in this position. None of the mutations affected the synthesis, oligomer formation, transport, or processing of the HIV glycoprotein complex. Although these results do not rule out a role for the leucine zipper region in glycoprotein oligomerization, they clearly point to a critical role for it in a post-CD4 binding step in HIV membrane fusion and virus entry.

Intracellular processing of the paramyxovirus F protein: critical role of the predicted amphipathic alpha helix adjacent to the fusion domain

At a nonpermissive temperature, the group D temperature-sensitive mutants of Newcastle disease virus strain Australia-Victoria (AV) are defective in plaque formation, in inducing infected cells to fuse, and in incorporating the cleaved fusion glycoprotein, F1 + F2, into virus particles. In this study, the F protein of AV, expressed in chicken embryo cells, was able to complement these mutants in a plaque assay, identifying the F gene as the gene containing the group D temperature-sensitive lesions. The F genes of mutants D1, D2, and D3 were found to contain single mutations relative to the AV sequence, clustered within a predicted amphipathic alpha helix (AAH) adjacent to the hydrophobic amino terminus of F1. These mutant F proteins were inefficiently processed at the permissive temperature, a problem that was exacerbated at the nonpermissive temperature. Surprisingly, the AV F protein was also found to be partially temperature sensitive in processing. Its AAH is predicted to contain a break in the helix close to the D mutation sites, which are themselves predicted to further weaken the helix at this point. Interestingly, six revertants of the group D mutants were found to have an additional lesion in the AAH, repairing both the AV and mutant helices, resulting in a predicted perfect helix. The F protein of these revertants had overcome both the processing defects of the mutants and the temperature sensitivity of AV, indicating that the AAH region is critical for F protein processing. The lesions of a second group of revertants were localized within F2, suggesting an interaction with the F1 AAH region containing the original lesion.

The fusion protein gene of phocine distemper virus: nucleotide and deduced amino acid sequences and a comparison of morbillivirus fusion proteins

The nucleotide sequence of the gene encoding the fusion protein of phocine distemper virus has been determined. The mRNA is 2206 nucleotides in length and contains one major open reading frame (ORF) of 1893 nucleotides encoding a potential protein of 631 amino acid residues. However, analogy with canine distemper virus (CDV) suggests that translation of the F protein starts at the sixth AUG codon in the mRNA sequence which is located at position 461, resulting in an F0 protein of exactly the same size (537 aa) as that of CDV. The overall homology at nucleotide level between the CDV and PDV F genes is 66%. The homology between the two F proteins of these respective viruses is 83%.

Molecular domains involved in oligomerization of the Friend murine leukemia virus envelope glycoprotein

The oligomeric structure of the Friend murine leukemia virus envelope glycoprotein has been investigated using crosslinking reagents and sucrose density gradient centrifugation. The results obtained provide evidence that both the precursor and the processed molecules are oligomeric and probably form tetramers. Pulse-chase analyses indicate that assembly occurs sequentially, within 30 min of protein synthesis and prior to cleavage of the precursor. Studies using chimeric envelope glycoproteins and deletion mutants indicate that the transmembrane and cytoplasmic domains are not essential for the formation of oligomers. Evidence is also presented that the SU subunit remains in an oligomeric form following disassociation from the TM subunit. Oligomeric envelope glycoprotein complexes linked by intermolecular disulfide bonds were also observed under certain conditions. Mink cell focus-forming virus envelope glycoprotein constructs lacking the transmembrane domain or both the transmembrane and the cytoplasmic domains formed intermolecular disulfide bonds more readily than the full-length molecule, suggesting that these regions are likely to make a contribution to the conformation of the glycoprotein. These data indicate that there are several points of interaction between retrovirus envelope glycoprotein monomers which contribute to assembly of the oligomer and that contacts within the ectodomain appear to be of critical importance.

Differential regulation of glucose transporter isoforms by the src oncogene in chicken embryo fibroblasts

The increase in glucose transport that occurs when chicken embryo fibroblasts (CEFs) are transformed by src is associated with an increase in the amount of type 1 glucose transporter protein, and we have previously shown that this effect is due to a decrease in the degradation rate of this protein. The rate of CEF type 1 glucose transporter biosynthesis and the level of its mRNA are unaffected by src transformation. To study the molecular basis of this phenomenon, we have been isolating chicken glucose transporter cDNAs by hybridization to a rat type 1 glucose transporter probe at low stringency. Surprisingly, these clones corresponded to a message encoding a protein which has most sequence similarity to the human type 3 glucose transporter and which we refer to as CEF-GT3. CEF-GT3 is clearly distinct from the CEF type 1 transporter that we have previously described. Northern (RNA) analysis of CEF RNA with CEF-GT3 cDNA revealed two messages of 1.7 and 3.3 kb which were both greatly induced by src transformation. When the CEF-GT3 cDNA was expressed in rat fibroblasts, a three-to fourfold enhancement of 2-deoxyglucose uptake was observed, indicating that CEF-GT3 is a functional glucose transporter. Northern analyses using a CEF-GT3 and a rat type 1 probe demonstrated that there is no hybridization between different isoforms but that there is cross-species hybridization between the rat type 1 probe and the chicken homolog. Southern blot analyses confirmed that the chicken genomic type 1 and type 3 transporters are encoded by distinct genes. We conclude that CEFs express two types of transporter, type 1 (which we have previously reported to be regulated posttranslationally by src) and a novel type 3 isoform which, unlike type 1, shows mRNA induction upon src transformation. We conclude that src regulates glucose transport in CEFs simultaneously by two different mechanisms.

Differential regulation of glucose transporter isoforms by the src oncogene in chicken embryo fibroblasts

The increase in glucose transport that occurs when chicken embryo fibroblasts (CEFs) are transformed by src is associated with an increase in the amount of type 1 glucose transporter protein, and we have previously shown that this effect is due to a decrease in the degradation rate of this protein. The rate of CEF type 1 glucose transporter biosynthesis and the level of its mRNA are unaffected by src transformation. To study the molecular basis of this phenomenon, we have been isolating chicken glucose transporter cDNAs by hybridization to a rat type 1 glucose transporter probe at low stringency. Surprisingly, these clones corresponded to a message encoding a protein which has most sequence similarity to the human type 3 glucose transporter and which we refer to as CEF-GT3. CEF-GT3 is clearly distinct from the CEF type 1 transporter that we have previously described. Northern (RNA) analysis of CEF RNA with CEF-GT3 cDNA revealed two messages of 1.7 and 3.3 kb which were both greatly induced by src transformation. When the CEF-GT3 cDNA was expressed in rat fibroblasts, a three-to fourfold enhancement of 2-deoxyglucose uptake was observed, indicating that CEF-GT3 is a functional glucose transporter. Northern analyses using a CEF-GT3 and a rat type 1 probe demonstrated that there is no hybridization between different isoforms but that there is cross-species hybridization between the rat type 1 probe and the chicken homolog. Southern blot analyses confirmed that the chicken genomic type 1 and type 3 transporters are encoded by distinct genes. We conclude that CEFs express two types of transporter, type 1 (which we have previously reported to be regulated posttranslationally by src) and a novel type 3 isoform which, unlike type 1, shows mRNA induction upon src transformation. We conclude that src regulates glucose transport in CEFs simultaneously by two different mechanisms.

A role for hydrophobic residues in the voltage-dependent gating of Shaker K+ channels

A leucine heptad repeat is well conserved in voltage-dependent ion channels. Herein we examine the role of the repeat region in Shaker K+ channels through substitution of the leucines in the repeat and through coexpression of normal and truncated products. In contrast to leucine-zipper DNA-binding proteins, we find that the subunit assembly of Shaker does not depend on the leucine heptad repeat. Instead, we report that substitutions of the leucines in the repeat produce large effects on the observed voltage dependence of conductance voltage and prepulse inactivation curves. Our results suggest that the leucines mediate interactions that play an important role in the transduction of charge movement into channel opening and closing.

A sequence preference for nucleation of alpha-helix--crystal structure of Gly-L-Ala-L-Val and Gly-L-Ala-L-Leu: some comments on the geometry of leucine zippers

The synthetic peptide Gly-L-Ala-L-Val (C10H19N3O4.3H2O; GAV) crystallizes in the monoclinic space group P21, with a = 8.052(2), b = 6.032(2), c = 15.779(7) A, beta = 98.520(1) degree, V = 757.8 A3, Dx = 1.312 g cm-3, and Z = 2. The peptide Gly-L-Ala-L-Leu (C11H21N3O4.3H2O; GAL) crystallizes in the orthorhombic space group P212121, with a = 6.024(1), b = 8.171(1), c = 32.791(1) A, V = 1614 A3, Dx = 1.289 g cm-3, and Z = 4. Their crystal structures were solved by direct methods using the program SHELXS-86, and refined to an R index of 0.05 for 1489 reflections for GAV and to an R index of 0.05 for 1563 reflections for GAL. The tripeptides exist as a zwitterion in the crystal and assume a near alpha-helical backbone conformation with the following torsion angles: psi 1 = -150.7 degrees; phi 2, psi 2 = -68.7 degrees, -38.1 degrees; phi 3, psi 32 = -74.8 degrees, -44.9 degrees, 135.9 degrees for GAV; psi 1 = -150.3 degrees; phi 2, psi 2 = -67.7 degrees, -38.9 degrees; phi 3, psi 31, psi 32 = -72.2 degrees, -45.3 degrees, 137.5 degrees for GAL. Both the peptide units in both of the tripeptides show significant deviation from planarity [omega 1 = -171.3(6) degrees and omega 2 = -172.0(6) degrees for GAV; omega 1 = -171.9(5) degrees and omega 2 = -173.2(6) degrees for GAL]. The side-chain conformational angles chi 21 and chi 22 are -61.7(5) degrees and 175.7(5) degrees, respectively, for valine, and the side-chain conformations chi 12 and chi 23's are -68.5(5) degrees and (-78.4(6) degrees, 159.10(5) degrees) respectively, for leucine. Each of the tripeptide molecule is held in a near helical conformation by a water molecule that bridges the NH3+ and COO- groups, and acts as the fourth residue needed to complete the turn by forming two hydrogen bonds. Two other water molecules form intermolecular hydrogen bonds in stabilizing the helical structure so that the end result is a column of molecules that looks like an alpha-helix.

Folding and function of the myelin proteins from primary sequence data

To explain how the myelin proteins are involved in the organization and function of the myelin sheath requires knowing their molecular structures. Except for P2 basic protein of PNS myelin, however, their structures are not yet known. As an aid to predicting their molecular folding and possible functions, we have developed a FORTRAN program to analyze the primary sequence data for proteins, and have applied this to the myelin proteins in particular. In this program, propensities for the secondary structure conformations as well as physical-chemical parameters are assigned to the amino acids and the pattern of these parameters is examined by calculating their average values, autocorrelation functions and Fourier transforms. To compare two proteins, their sequences are aligned using a unitary scoring matrix, and homologies are searched by plotting a two-dimensional map of the correlation coefficients. Comparison of the corresponding myelin basic proteins (MBP) and P0 glycoproteins (P0) for rodent and shark showed that the conserved residues included most of the amino acids which were predicted to form the alpha or beta conformations, while the altered residues were mainly in the hydrophilic and turn or coil regions. In both rodent and shark the putative extracellular domain of P0 glycoprotein displayed consecutive peaks of beta propensity similar to that for the immunoglobulins, while the cytoplasmic domain showed alpha-beta-alpha folding. To trace the immunoglobulin fold along the P0 sequence, we compared the beta propensity curve of P0 with that of the immunoglobulin M603, whose three-dimensional structure has been determined. We propose that the flat beta-sheets of P0 are orientated parallel to the membrane surface to facilitate their homotypic interaction in the extracellular space. An extra beta-fold in the extracellular domain of shark P0 compared with rodent P0 was found, and this may result in a greater attraction between the apposed extracellular surfaces and may account for a smaller extracellular space as measured by x-ray diffraction. A computer search of the myelin protein sequences for functional motifs revealed sites for N-glycosylation, phosphorylation, nucleotide binding, and certain enzyme activities. We note especially that there are potential nucleotide binding sites in proteolipid protein (PLP), MBP and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP). This is consistent with the experimental observations that PLP acts like an ionophore or proton channel when reconstituted into planar lipid bilayers, MBP binds GTP, and CNP catalyzes in vitro the hydrolysis of 2',3'-nucleotides into corresponding 2'-nucleotides.

Sequence of swallow, a gene required for the localization of bicoid message in Drosophila eggs

We report the sequence of the Drosophila maternal effect gene swallow, one of the genes whose product is required for the localization of bicoid message during Drosophila oogenesis. The inferred swallow protein contains a domain that is predicted to be an amphipathic alpha-helix similar to those implicated in protein:protein associations in other systems. Another part of the predicted protein appears to be a diverged RNA-binding motif. We discuss these structural features in light of the function of the swallow protein in the bicoid message localization process.

Evi-2, a common integration site involved in murine myeloid leukemogenesis

BXH-2 mice have the highest incidence of spontaneous retrovirally induced myeloid leukemia of any known inbred strain and, as such, represent a valuable model system for identifying cellular proto-oncogenes involved in myeloid disease. Chronic murine leukemia viruses often induce disease by insertional activation or mutation of cellular proto-oncogenes. These loci are identified as common viral integration sites in tumor DNAs. Here we report on the characterization of a novel common viral integration site in BXH-2 myeloid leukemias, designated Evi-2. Within the cluster of viral integration sites that define Evi-2, we identified a gene that has the potential for encoding a novel protein of 223 amino acids. This putative proto-oncogene possesses all of the structural features of a transmembrane protein. Within the transmembrane domain is a "leucine zipper," suggesting that Evi-2 is involved in either homopolymer or heteropolymer formation, which may play an important role in the normal functioning of Evi-2. Interestingly, the human homolog of Evi-2 has recently been shown to be tightly linked to the von Recklinghausen neurofibromatosis locus, suggesting a role for Evi-2 in human disease as well.

Sequence of the fusion protein gene of human parainfluenza type 2 virus and its 3' intergenic region: lack of small hydrophobic (SH) gene

cDNA clones representing the fusion (F) gene of human parainfluenza virus type 2 (PIV-2) were isolated from cDNA libraries constructed from virus-specific mRNA and genomic RNA, and the complete nucleotide sequence of the F gene was determined. The F gene is 1854 nucleotides long and encodes one long open reading frame of 551 amino acids. The cleavage site for activation of the precursor Fo protein is Thr-Arg-Gln-Lys-Arg. The F gene of PIV-2 is most closely related to those of simian virus 5 (SV5) and mumps virus (MuV). Interestingly, although the HN glycoprotein of PIV-2 shows no relatedness to the HA glycoprotein of measles virus (MV), a distinct homology is found in the F proteins of PIV-2 and MV. As concerns F proteins, paramyxoviruses can be divided into two subgroups; that is, PIV-2, SV5, and MuV belong to one group, and HPIV-1, SV, and PIV-3 belong to the other group. Newcastle disease virus (NDV) and MV are intermediate. Coding regions for small hydrophobic (SH) proteins have been found between the HN and F genes of SV5 and MuV, which are the viruses most closely related to PIV-2. However, such a gene could not be detected in two different strains of PIV-2.

Evi-2, a common integration site involved in murine myeloid leukemogenesis

BXH-2 mice have the highest incidence of spontaneous retrovirally induced myeloid leukemia of any known inbred strain and, as such, represent a valuable model system for identifying cellular proto-oncogenes involved in myeloid disease. Chronic murine leukemia viruses often induce disease by insertional activation or mutation of cellular proto-oncogenes. These loci are identified as common viral integration sites in tumor DNAs. Here we report on the characterization of a novel common viral integration site in BXH-2 myeloid leukemias, designated Evi-2. Within the cluster of viral integration sites that define Evi-2, we identified a gene that has the potential for encoding a novel protein of 223 amino acids. This putative proto-oncogene possesses all of the structural features of a transmembrane protein. Within the transmembrane domain is a "leucine zipper," suggesting that Evi-2 is involved in either homopolymer or heteropolymer formation, which may play an important role in the normal functioning of Evi-2. Interestingly, the human homolog of Evi-2 has recently been shown to be tightly linked to the von Recklinghausen neurofibromatosis locus, suggesting a role for Evi-2 in human disease as well.

The role of the 5' nontranslated regions of the fusion protein mRNAs of canine distemper virus and rinderpest virus

The mRNAs which code for the fusion proteins of the morbilliviruses (measles virus, canine distemper virus, and rinderpest virus) have unusually long 5' untranslated regions (UTRs) which are GC-rich and are capable of folding into extensive secondary structures. In measles virus the first AUG codons in the fusion (F) protein mRNA are in close proximity at nucleotide positions 574 and 583 and protein translation is initiated at the second position. In the canine distemper virus (CDV) and rinderpest virus (RPV) F gene transcripts the analogous initiation codons are preceded by several other AUG codons many nucleotides upstream either in the same reading frame or at the beginning of other short open reading frames. We have studied the effect of deleting these upstream regions on the production of the fusion proteins of both CDV and RPV from cDNA constructs. Within the cells the presence of these regions enhances the production of the F protein while, in contrast, the production of the authentic F protein from in vitro translations using RNA transcripts is inhibited by these sequences.

Photosystem I reaction-centre proteins contain leucine zipper motifs. A proposed role in dimer formation

The photosystem I (PS I) reaction-centre polypeptides, encoded by the psaA and psaB genes, are shown to contain several highly conserved leucine repeats, consisting of a leucine residue every seventh amino acid, similar to the leucine zipper motifs known to mediate DNA-binding polypeptide dimerisation. In each of the PSI reaction-centre subunits the leucine zipper motif precedes highly conserved cysteine residues which have been proposed to ligate the interpolypeptide [4Fe-4S] centre, Fx. We propose that PS I reaction-centre dimerisation and [4Fe-4S] centre formation are mediated through the leucine zipper.

Sequence and molecular characterization of a multicopy invasion plasmid antigen gene, ipaH, of Shigella flexneri

A lambda gt11 expression library of Tn5-tagged invasion plasmid pWR110 (from Shigella flexneri serotype 5, strain M90T-W) contained a set of recombinants encoding a 60-kilodalton protein (designated IpaH) recognized by rabbit antisera raised against S. flexneri invasion plasmid antigens (J. M. Buysse, C. K. Stover, E. V. Oaks, M. M. Venkatesan, and D. J. Kopecko, J. Bacteriol. 169:2561-2569, 1987). Southern blot analysis of wild-type S. flexneri serotype 5 invasion plasmid DNA (pWR100) digested with various combinations of five restriction enzymes and hybridized with defined ipaH probes showed complex hybridization patterns resulting from multiple copies of the ipaH gene on pWR100. DNA sequence analysis of a 2.9-kilobase (kb) EcoRI fragment directing IpaH antigen synthesis in plasmid recombinant pWR390 revealed an open reading frame coding for a 532-amino-acid protein (60.8 kilodaltons); this size matched well with the estimated size of IpaH determined by Western blot analysis of M90T-W cells and maxicell analysis of Escherichia coli HB101(pWR390) transformants. Examination of the amino acid sequence of IpaH revealed a hydrophilic protein with six evenly spaced 14-residue (L-X2-L-P-X-L-P-X2-L-X2-L) repeat motifs in the amino-terminal end of the molecule. Southern blot analysis of HindIII-digested pWR100 DNA probed with defined segments of the pWR390 2.9-kb insert demonstrated that the multiple band hybridization pattern resulted from repeats of a significant portion of the ipaH structural gene in five distinct HindIII fragments (9.8, 7.8, 4.5, 2.5, and 1.4 kb). Affinity-purified IpaH antibody, used to monitor the expression of the antigen in M90T-W cells grown at 30 and 37 degrees C, showed that IpaH synthesis was not regulated by growth temperature.

Molecular cloning and complete nucleotide sequence of the attenuated rabies virus SAD B19

Complementary DNA spanning the entire genome of the attenuated rabies virus strain SAD B19 which is used for oral immunization of foxes in Europe was cloned and sequenced. The viral genome comprises 11,928 nucleotides and encodes the five viral proteins N, NS, M, G, and L. Deduced protein sequences are highly similar to those of the pathogenic PV strain, homologies ranging from 90.6% for the M to 98.6% for the L protein. The five cistrons are separated by intergenic regions of 2, 5, 5, and 24 nucleotides, respectively. The G transcription stop/polyadenylation consensus signal in SAD B19 is destroyed by a deletion of three A residues. The strong conservation of both noncoding and coding nucleotide sequences indicates a high selective pressure on the primary structure of rabies virus genomic RNA.

Dimers, leucine zippers and DNA-binding domains

Transcription factors can be divided into classes on the basis of their mode of interaction with the target promoter sequence. Different protein domains responsible for DNA recognition have been identified. In this review we discuss the leucine zipper structure, which has been found in several nuclear factors, including the oncoproteins Fos and Jun. Structural considerations are summarized to help understand how dimerization is mediated by the leucine zipper and how this is the prerequisite for optimal target DNA recognition by the adjacent basic domains.