Molecular structure of a gene, VMA1, encoding the catalytic subunit of H(+)-translocating adenosine triphosphatase from vacuolar membranes of Saccharomyces cerevisiae

Molecular cloning and characterization of the B subunit of a vacuolar H(+)-ATPase from the midgut and Malpighian tubules of Helicoverpa virescens

Using the polymerase chain reaction (PCR) a 0.8-kb product was amplified from cDNA made from the midgut and Malpighian tubules of fifth instar larvae of Helicoverpa virescens. This 0.8-kb PCR product was then used to isolate a clone of the B subunit of the V-type ATPase from a cDNA library made from the same tissues. The cDNA clone encodes for a protein of 55 kDa which shows very high amino acid homology to other known B subunits of V-type ATPases. The transcript size of the B subunit in the midgut of H. virescens was 2.3 kb, and a transcript of identical size was also detected in the Malpighian tubules. Northern blot analysis revealed the presence of a homologous transcript of 2.6 kb in the midgut of Manduca sexta and PCR analysis also confirmed the presence of such a transcript in the Malpighian tubules and the nervous system of M. sexta, and in the midgut Malpighian tubules of Culex quinquefasciatus. The presence of the V-type ATPase in the Malpighian tubules of lepidopteran insects suggests that the transport of ions across the cell membrane in this tissue is also probably driven by a similar process as that observed in the midgut of these insects.

Novel structure of the recA locus of Mycobacterium tuberculosis implies processing of the gene product

A fragment of Mycobacterium tuberculosis DNA containing recA-like sequences was identified by hybridization with the Escherichia coli recA gene and cloned. Although no expression was detected from its own promoter in E. coli, expression from a vector promoter partially complemented E. coli recA mutants for recombination, DNA repair, and mutagenesis, but not for induction of phage lambda. This clone produced a protein which cross-reacts with antisera raised against the E. coli RecA protein and was approximately the same size. However, the nucleotide sequence of the cloned fragment revealed the presence of an open reading frame for a protein about twice the size of other RecA proteins and the cloned product detected by Western blotting (immunoblotting). The predicted M. tuberculosis RecA protein sequence was homologous with RecA sequences from other bacteria, but this homology was not dispersed; rather it was localized to the first 254 and the last 96 amino acids, with the intervening 440 amino acids being unrelated. Furthermore, the junctions of homology were in register with the uninterrupted sequence of the E. coli RecA protein. Identical restriction fragments were found in the genomic DNAs of M. tuberculosis H37Rv and H37Ra and of M. bovis BCG. It is concluded that the ancestral recA gene of these species diversified via an insertional mutation of at least 1,320 bp of DNA. Possible processing mechanisms for synthesizing a normal-size RecA protein from this elongated sequence are discussed.

The GTP-binding Sar1 protein is localized to the early compartment of the yeast secretory pathway

SAR1, the yeast gene which encodes a novel type of small GTP-binding protein, has been shown to be required for protein transport from the endoplasmic reticulum (ER) to the Golgi apparatus. To further the understanding of the function of its product, a lacZ-SAR1 hybrid gene was constructed and a polyclonal antibody was raised against the hybrid protein. This antibody specifically recognizes the SAR1 gene product (Sar1p) as a 23-kDa protein in the yeast cell lysate. We examined the subcellular localization of Sar1p using this antibody. In wild-type cells, Sar1p was predominantly recovered in a rapidly sedimenting membrane fraction that includes the ER. The soluble form of Sar1p was also detected when the protein was overproduced. Immunofluorescence microscopy with the anti-Sar1p antibody showed perinuclear staining that was exaggerated in the ER-accumulating sec18 mutant. Membrane association of Sar1p was shown to be very light. Sar1p was not extracted from the membrane by treatment with alkaline sodium carbonate, and only 1% deoxycholic acid solubilized Sar1p completely. From these results, we suggest that Sar1p is firmly located on the ER membrane where it regulates the ER-Golgi traffic.

MAP1B is encoded as a polyprotein that is processed to form a complex N-terminal microtubule-binding domain

Microtubule-associated protein 1B (MAP1B), an abundant developmentally regulated neuronal protein, is a stoichiometric complex of a heavy chain and two light chains (light chain 1 and light chain 3). We find that light chain 1 is encoded within the 3' end of a previously reported MAP1B heavy chain cDNA. Amino acid sequencing, epitope mapping, Northern blotting, and Southern blotting indicate that the light chain and heavy chain are encoded by the same mRNA within the same open reading frame. In addition, amino acid sequencing of a 120 kd microtubule-binding and light chain-binding fragment of the heavy chain reveals that light chain 1 binds near the heavy chain N-terminus. Together these data indicate that the heavy chain and light chain 1 are produced by proteolytic processing of a MAP1B polyprotein and form a complex microtubule-binding domain.

The ATP synthase of Halobacterium salinarium (halobium) is an archaebacterial type as revealed from the amino acid sequences of its two major subunits

The head piece of the A-type ATP synthase in an extremely halophilic archaebacterium, namely Halobacterium salinarium (halobium), is composed of two kinds of subunit, alpha and beta, and is associated with ATP-hydrolyzing activity. The genes encoding these subunits with hydrolytic activity have been cloned and sequenced. The putative amino acid sequences of the alpha and beta subunits deduced from the nucleotide sequences of the genomic DNA consist of 585 and 471 residues, respectively. The amino acid sequence of the alpha subunit of the halobacterial ATPase is 63 and 49% identical to the alpha subunits of ATPases from two other archaebacteria, Methanosarcina barkeri and Sulfolobus acidocaldarius, respectively. The sequence of the beta subunit is 66 and 55% identical to the beta subunits from these respective organisms. The homology between the alpha and beta subunits is around 30%. In contrast, the sequences of the halobacterial ATPase is less than 30% identical to F1 ATPase when any combination of subunits is considered. However, they are greater than 50% identical to a eukaryotic vacuolar ATPase when alpha and a, beta and b combinations are considered. These data fully confirm the first demonstration of this kind of relationship which was achieved by immunoblotting with an antibody raised against the halobacterial ATPase. We concluded that the archaebacterial ATP synthase is an A-type and not an F-type ATPase. This classification is also demonstrated by a "rooted" phylogenetic tree where halobacteria locate close to other archaebacteria and eukaryotes and distant from eubacteria.

The ATP-binding site of the human placental H+ pump contains essential tyrosyl residues

Transient exposure of human placental brush-border membrane vesicles to cholate reorients the ATP-driven H+ pump, enabling the pump to transport H+ into the vesicles upon addition of ATP to the external medium. H+ uptake can be measured in these vesicles by following the decrease in the absorbance of acridine orange, a delta pH indicator. We investigated the role of tyrosyl residues in the catalytic function of the H+ pump by studying the effects of tyrosyl group specific reagents on ATP-driven H+ uptake in cholate-pretreated membrane vesicles. The reagents tested were 7-chloro-4-nitro-2,1,3-benzoxadiazole (NBD-Cl), N-acetylimidazole, tetranitromethane, and p-nitrobenzenesulfonyl fluoride. Treatment of the membrane vesicles with these reagents resulted in the inhibition of the ATP-driven H+ uptake, and the inhibitory potency was in the following order: NBD-Cl greater than tetranitromethane greater than p-nitrobenzenesulfonyl fluoride greater than N-acetylimidazole. The inhibition of the H+ pump by NBD-Cl was reversible by 2-mercaptoethanol, and the inhibition by N-acetylimidazole was reversible by hydroxylamine. Since these reagents are not absolutely specific for tyrosyl groups and can also react with thiol groups, we studied the interaction of N-acetylimidazole with the H+ pump whose triol groups were masked by reaction with p-(chloromercuri)benzenesulfonate. The SH-masked pump was totally inactive, but the activity could be restored by dithiothreitol. On the contrary, the activity of the SH-masked H+ pump which was subsequently treated with N-acetylimidazole could not be restored by dithiothreitol, suggesting that thiol groups were not involved in the inhibition of the H+ pump by N-acetylimidazole.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein splicing converts the yeast TFP1 gene product to the 69-kD subunit of the vacuolar H(+)-adenosine triphosphatase

The TFP1 gene of the yeast Saccharomyces cerevisiae encodes two proteins: the 69-kilodalton (kD) catalytic subunit of the vacuolar proton-translocating adenosine triphosphatase (H(+)-ATPase) and a 50-kD protein. The 69-kD subunit is encoded by the 5' and 3' thirds of the TFP1 coding region, whereas the 50-kD protein is encoded by the central third. Evidence is presented that both the 69-kD and 50-kD proteins are obtained from a single translation product that is cleaved to release the 50-kD protein and spliced to form the 69-kD subunit.