Self-assembly of mesoscopically ordered chromatic polydiacetylene/silica nanocomposites

Nature abounds with intricate composite architectures composed of hard and soft materials synergistically intertwined to provide both useful functionality and mechanical integrity. Recent synthetic efforts to mimic such natural designs have focused on nanocomposites, prepared mainly by slow procedures like monomer or polymer infiltration of inorganic nanostructures or sequential deposition. Here we report the self-assembly of conjugated polymer/silica nanocomposite films with hexagonal, cubic or lamellar mesoscopic order using polymerizable amphiphilic diacetylene molecules as both structure-directing agents and monomers. The self-assembly procedure is rapid and incorporates the organic monomers uniformly within a highly ordered, inorganic environment. Polymerization results in polydiacetylene/silica nanocomposites that are optically transparent and mechanically robust. Compared to ordered diacetylene-containing films prepared as Langmuir monolayers or by Langmuir-Blodgett deposition, the nanostructured inorganic host alters the diacetylene polymerization behaviour, and the resulting nanocomposite exhibits unusual chromatic changes in response to thermal, mechanical and chemical stimuli. The inorganic framework serves to protect, stabilize, and orient the polymer, and to mediate its function. The nanocomposite architecture also provides sufficient mechanical integrity to enable integration into devices and microsystems.

Regulated expression of the obese gene product (leptin) in white adipose tissue and 3T3-L1 adipocytes

A mutation within the obese gene was recently identified as the genetic basis for obesity in the ob/ob mouse. The obese gene product, leptin, is a 16-kDa protein expressed predominantly in adipose tissue. Consistent with leptin's postulated role as an extracellular signaling protein, human embryonic kidney 293 cells transfected with the obese gene secreted leptin with minimal intracellular accumulation. Upon differentiation of 3T3-L1 preadipocytes into adipocytes, the leptin mRNA was expressed concomitant with mRNAs encoding adipocyte marker proteins. A factor(s) present in calf serum markedly activated expression of leptin by fully differentiated 3T3-L1 adipocytes. A 16-hr fast decreased (by approximately 85%) the leptin mRNA level of adipose tissue of lean (ob/+ or +/+) mice but had no effect on the approximately 4-fold higher level in obese (ob/ob) littermates. Since the mutation at the ob locus fails to produce the functional protein, yet its cognate mRNA is overproduced, it appears that leptin is necessary for its own downregulation. Leptin mRNA was also suppressed in adipose tissue of rats during a 16-hr fast and was rapidly induced during a 4-hr refeeding period. Insulin deficiency provoked by streptozotocin also markedly down-regulated leptin mRNA and this suppression was rapidly reversed by insulin. These results suggest that insulin may regulate the expression of leptin.

Specific substitutions in the echinocandin target Fks1p account for reduced susceptibility of rare laboratory and clinical Candida sp. isolates

An association between reduced susceptibility to echinocandins and changes in the 1,3-beta-d-glucan synthase (GS) subunit Fks1p was investigated. Specific mutations in fks1 genes from Saccharomyces cerevisiae and Candida albicans mutants are described that are necessary and sufficient for reduced susceptibility to the echinocandin drug caspofungin. One group of amino acid changes in ScFks1p, ScFks2p, and CaFks1p defines a conserved region (Phe 641 to Asp 648 of CaFks1p) in the Fks1 family of proteins. The relationship between several of these fks1 mutations and the phenotype of reduced caspofungin susceptibility was confirmed using site-directed mutagenesis or integrative transformation. Glucan synthase activity from these mutants was less susceptible to caspofungin inhibition, and heterozygous and homozygous Cafks1 C. albicans mutants could be distinguished based on the shape of inhibition curves. The C. albicans mutants were less susceptible to caspofungin than wild-type strains in a murine model of disseminated candidiasis. Five Candida isolates with reduced susceptibility to caspofungin were recovered from three patients enrolled in a clinical trial. Four C. albicans strains showed amino acid changes at Ser 645 of CaFks1p, while a single Candida krusei isolate had a deduced R1361G substitution. The clinical C. albicans mutants were less susceptible to caspofungin in the disseminated candidiasis model, and GS inhibition profiles and DNA sequence analyses were consistent with a homozygous fks1 mutation. Our results indicate that substitutions in the Fks1p subunit of GS are sufficient to confer reduced susceptibility to echinocandins in S. cerevisiae and the pathogens C. albicans and C. krusei.

The rate of nuclear cytoplasmic protein transport is determined by the casein kinase II site flanking the nuclear localization sequence of the SV40 T-antigen

We have previously demonstrated [Rihs, H.-P. and Peters, R. (1989) EMBO J., 8, 1479-1484] that the nuclear transport of recombinant proteins in which short fragments of the SV40 T-antigen are fused to the amino terminus of Escherichia coli beta-galactosidase is dependent on both the nuclear localization sequence (NLS, T-antigen residues 126-132) and a phosphorylation-site-containing sequence (T-antigen residues 111-125). While the NLS determines the specificity, the rate of transport is controlled by the phosphorylation-site-containing sequence. The present study furthers this observation and examines the role of the various phosphorylation sites. Purified, fluorescently labeled recombinant proteins were injected into the cytoplasm of Vero or hepatoma (HTC) cells and the kinetics of nuclear transport measured by laser microfluorimetry. By replacing serine and threonine residues known to be phosphorylated in vivo, we identified the casein kinase II (CK-II) site S111/S112 to be the determining factor in the enhancement of the transport. Either of the residues 111 or 112 was sufficient to elicit the maximum transport enhancement. The other phosphorylation sites (S120, S123, T124) had no influence on the transport rate. Examination of the literature suggested that many proteins harboring a nuclear localization sequence also contain putative CK-II sites at a distance of approximately 10-30 amino acid residues from the NLS. CK-II has been previously implicated in the transmission of growth signals to the nucleus. Our results suggest that CK-II may exert this role by controlling the rate of nuclear protein transport.

Non-function of a Moloney murine leukaemia virus regulatory sequence in F9 embryonal carcinoma cells

Moloney murine leukaemia virus (M-MuLV) infection of embryonal carcinoma (EC) cells results in the integration of proviral DNA into the host cell genome, but not in virus production. One suggested explanation for the lack of viral gene expression in EC cells has been methylation of the integrated viral DNA. However, subsequent reports indicated that integration of the M-MuLV DNA occurs soon after infection, but that viral DNA methylation occurs considerably later. Nevertheless, viral gene expression is not observed even at early times. One possible explanation is that certain M-MuLV regulatory sequences do not function in EC cells. We now present evidence which supports this hypothesis.

Induction of basal cell carcinoma features in transgenic human skin expressing Sonic Hedgehog

Hedgehog (HH) signaling proteins mediate inductive events during animal development. Mutation of the only known HH receptor gene, Patched (PTC), has recently been implicated in inherited and sporadic forms of the most common human cancer, basal cell carcinoma (BCC). In Drosophila, HH acts by inactivating PTC function, raising the possibility that overexpression of Sonic Hedgehog (SHH) in human epidermis might have a tumorigenic effect equivalent to loss of PTC function. We used retroviral transduction of normal human keratinocytes to constitutively express SHH. SHH-expressing cells demonstrated increased expression of both the known HH target, BMP-2B, as well as bcl-2, a protein prominently expressed by keratinocytes in BCCs. These keratinocytes were then used to regenerate human skin transgenic for long terminal repeat-driven SHH (LTR-SHH) on immune-deficient mice. LTR-SHH human skin consistently displays the abnormal specific histologic features seen in BCCs, including downgrowth of epithelial buds into the dermis, basal cell palisading and separation of epidermis from the underlying dermis. In addition, LTR-SHH skin displays the gene expression abnormalities previously described for human BCCs, including decreased BP180/BPAG2 and laminin 5 adhesion proteins and expression of basal epidermal keratins. These data indicate that expression of SHH in human skin recapitulates features of human BCC in vivo, suggest that activation of this conserved signaling pathway contributes to the development of epithelial neoplasia and describe a new transgenic human tissue model of neoplasia.

Ectodomain shedding of TGF-alpha and other transmembrane proteins is induced by receptor tyrosine kinase activation and MAP kinase signaling cascades

A variety of transmembrane proteins, such as transforming growth factor-alpha (TGF-alpha), tumor necrosis factor-alpha (TNF-alpha) and L-selectin, undergo shedding, i.e. cleavage of the ectodomain, resulting in release of a soluble protein. Although the physiological relevance of ectodomain shedding is well recognized, little is known about the signaling mechanisms activating this process. We show that growth factor activation of cell surface tyrosine kinase receptors induces ectodomain cleavage of transmembrane TGF-alpha through activation of the Erk MAP kinase signaling cascade without the need for new protein synthesis. In addition, expression of constitutively activated MEK1 or its downstream target Erk2 MAP kinase was sufficient to stimulate TGF-alpha shedding. The basal cleavage level in the absence of exogenous growth factor stimulation was due to p38 MAP kinase signaling. Accordingly, a constitutively activated MKK6, a p38 activator, activated TGF-alpha shedding in the absence of exogenous stimuli. In addition to TGF-alpha shedding, these mechanisms also mediate L-selectin and TNF-alpha cleavage. Thus, L-selectin shedding by neutrophils, induced by N-formylmethionyl-leucyl-phenylalanine, was strongly inhibited by inhibitors of Erk MAP kinase or p38 MAP kinase signaling. Our results indicate that activation of Erk and p38 signaling pathways may represent a general physiological mechanism to induce shedding of a variety of transmembrane proteins.

In vitro and in vivo binding of human immunodeficiency virus type 1 Tat protein and Sp1 transcription factor

Recent genetic experiments have suggested that tat transactivation of the human immunodeficiency virus type 1 (HIV-1) long terminal repeat requires functional upstream enhancer sequences--Sp1 sites, in particular. In these experiments, HeLa cell nuclear extracts were passed over affinity matrices containing chemically synthesized or bacterially expressed HIV-1 Tat. Assay of material that bound to and eluted from the Tat matrices revealed the presence of the Sp1 transcription factor. Other transcription factors (Oct and NF-kappa B) also bound to Tat matrices but with less efficiency--in parallel with the lower capacities of these binding motifs to confer Tat responsiveness on a basal HIV-1 promoter compared with Sp1 sites. Passage of nuclear extracts over matrices containing other neutral proteins, including bovine serum albumin, ovalbumin, and lysozyme, revealed no or reduced binding. Cross-linking experiments indicated that the purified Sp1 and Tat proteins can form multimeric complexes in the absence of other proteins. The region of Tat responsible for Sp1 binding was localized to a region encompassing residues 30 to 62. Immunoprecipitation experiments with HIV-1-infected T lymphocytes indicated coimmunoprecipitation of Tat and Sp1. These experiments extend previous genetic experiments and suggest a direct interaction between Tat and Sp1 during transactivation.

Jaagsiekte sheep retrovirus is necessary and sufficient to induce a contagious lung cancer in sheep

Sheep pulmonary adenomatosis (SPA) is a contagious and experimentally transmissible lung cancer of sheep resembling human bronchiolo-alveolar carcinoma. A type D retrovirus, known as jaagsiekte sheep retrovirus (JSRV), has been associated with the etiology of SPA, but its exact role in the induction of the tumor has not been clear due to the lack of (i) a tissue culture system for the propagation of JSRV and (ii) an infectious JSRV molecular clone. To investigate the role of JSRV in the etiology of SPA, we isolated a full-length JSRV proviral clone, pJSRV21, from a tumor genomic DNA library derived from a natural case of SPA. pJSRV21 was completely sequenced and showed open reading frames in agreement with those deduced for the original South African strain of JSRV. In vivo transfection of three newborn lambs by intratracheal inoculation with pJSRV21 DNA complexed with cationic lipids showed that pJSRV21 is an infectious molecular clone. Viral DNA was detected in the peripheral blood mononuclear cells (PBMCs) of the transfected animals by a highly sensitive JSRV-U3 heminested PCR at various time points ranging from 2 weeks to 6 months posttransfection. In addition, proviral DNA was detected in the PBMCs, lungs, and mediastinal lymph nodes of two lambs sacrificed 9 months posttransfection, but no macroscopic or histological SPA lesion was induced. We prepared JSRV particles by transient transfection of 293T cells with a JSRV construct (pCMV2JS21) in which the upstream U3 was replaced with the cytomegalovirus early promoter. Four newborn lambs were inoculated with JSRV21 particles produced in this manner, and two of them showed the classical signs of SPA 4 months postinfection. The resulting tumors were positive for JSRV DNA and protein. Thus, JSRV21 is an infectious and pathogenic molecular clone and is necessary and sufficient to induce sheep pulmonary adenomatosis.

Bradyrhizobium liaoningense sp. nov., isolated from the root nodules of soybeans

Seventeen strains of extra-slowly growing (ESG) soybean rhizobia isolated from root nodules of Glycine soja and Glycine max growing in five provinces (Liaoning, Heilongjiang, Shanxi, Hubei, and Anhui) in the People's Republic of China were compared with 48 reference strains belonging to the genera Bradyrhizobium, Rhizobium, and Agrobacterium by performing a numerical analysis of 191 phenotypic features. Our results showed that all of the ESG strains examined clustered closely in the genus Bradyrhizobium but were separated from Bradyrhizobium japonicum at the species level and that they could be differentiated from Rhizobium and Agrobacterium species at the genus level. On the basis of the results of our numerical taxonomy analysis, a genomic DNA G & C content analysis, DNA-DNA hybridization experiments, a partial 16S rRNA sequence analysis, a serological analysis, an N and C content analysis, and an N/C ratio analysis of members of the three groups of soybean rhizobia, we propose the name Bradyrhizobium liaoningense sp. nov. for the ESG strains; the type strain of this species is strain 2281.

Measurement of the sequence complexity of cloned Moloney murine leukemia virus 60 to 70S RNA: evidence for a haploid genome

The sequence complexity of the 60-70S RNA complex from Moloney murine leukemia virus (M-MuLV) was determined by measuring the annealing rate of radioactively labeled virus-specific DNA with M-MuLV 60-70S RNA in conditions of vast RNA excess. The M-MuLV RNA annealing rate, characterized by the quantity C(r)t((1/2)), was compared with the C(r)t((1/2)) values for annealing of poliovirus 35S RNA (2.6 x 10(6) molecular weight) with poliovirus-specific DNA and Sindbis virus 42S RNA (4.3 x 10(6) molecular weight) with Sindbis-specific DNA. M-MuLV-specific DNA was prepared in vitro by the endogenous DNA polymerase reaction of M-MuLV virions, and poliovirus and Sindbis virus DNAs were prepared by incubation of viral RNA and DNA polymerase purified from avian myeloblastosis virus and an oligo deoxynucleotide primer. The poliovirus and Sindbis virus DNAs were sedimented through alkaline sucrose gradients, and those portions of the DNA with sizes similar to the M-MuLV DNA were selected out for the annealing measurements. M-MuLV was cloned on NIH-3T3 cells because it appeared possible that the standard source of M-MuLV for these experiments was a mixture of viruses. The annealing measurements indicated a sequence complexity of approximately 9 x 10(6) daltons for the cloned M-MuLV 60-70S RNA when standardized to poliovirus and Sindbis virus RNAs. This value supports the hypothesis that each of the 35S RNA subunits of M-MuLV 60-70S RNA has a different base sequence.

Immunization via hair follicles by topical application of naked DNA to normal skin

In order to test the immune response generated to small amounts of foreign protein in skin, we applied naked DNA in aqueous solution to untreated normal skin. Topical application of plasmid expression vectors for lacZ and the hepatitis B surface antigen (HBsAg) to intact skin induced antigen-specific immune responses that displayed TH2 features. For HBsAg, specific antibody and cellular responses were induced to the same order of magnitude as those produced by intramuscular injection of the commercially available recombinant HBsAg polypeptide vaccine. Finally, topical gene transfer was dependent on the presence of normal hair follicles.

Optically defined multifunctional patterning of photosensitive thin-film silica mesophases

Photosensitive films incorporating molecular photoacid generators compartmentalized within a silica-surfactant mesophase were prepared by an evaporation-induced self-assembly process. Ultraviolet exposure promoted localized acid-catalyzed siloxane condensation, which can be used for selective etching of unexposed regions; for "gray-scale" patterning of refractive index, pore size, surface area, and wetting behavior; and for optically defining a mesophase transformation (from hexagonal to tetragonal) within the film. The ability to optically define and continuously control both structure and function on the macro- and mesoscales is of interest for sensor arrays, nanoreactors, photonic and fluidic devices, and low-dielectric-constant films.

Electrical stimulation induces the level of TGF-beta1 mRNA in osteoblastic cells by a mechanism involving calcium/calmodulin pathway

It is well-known that electrical stimulation can prompt healing of bone fractures. However, the mechanism involved is less clear. In this study, we found that capacitively coupled electric field-induced proliferation of osteoblastic cells (MC3T3-E1) accompanied increased levels of transforming growth factor-beta 1 (TGF-beta1) mRNA determined by quantitative reverse transcription/polymerase chain reaction. Previous reports have shown that verapamil and W-7, both of which block voltage gated calcium channels and inhibit the activation of cytosolic calmodulin, respectively, blocked capacitively coupled electric field-induced proliferation of the osteoblast cells. Interestingly, we found that verapamil and W-7 can also block capacitively coupled electric field-induced elevation of TGF-beta1 mRNA. This result suggested that electrical stimulation induces the level of TGF-beta1 mRNA in osteoblastic cells by a mechanism involving calcium/calmodulin pathway. The potential roles of TGF-beta in the electrical signal-induced osteogenesis was discussed.

Infection of preimplantation mouse embryos and of newborn mice with leukemia virus: tissue distribution of viral DNA and RNA and leukemogenesis in the adult animal

Explanted mouse embryos derived from low leukemia incidence strains were infected with Moloney murine leukemia virus (M-MuLV) at the 4-8 cell stage of development. After cultivation in vitro to the blastocyst stage, the embryos were surgically transferred to the uteri of pseudo-pregnant surrogate mothers. Of 15 animals born, one developed a leukemia at 8 weeks of age. When autopsied, this leukemia was found to be of the lymphatic type, as is typical for the M-MuLV-induced disease. In addition, infectious M-MuLV virus was isolated from the serum. Molecular hybridization tests for the presence of M-MuLV-specific sequences were conducted on DNA and RNA extracted from eight different organs. The DNA-DNA reannealing experiments revealed the presence of two classes of M-MuLV-specific sequences in equal concentrations in all tissues tested. The less abundant class of M-MuLV-specific sequences was not detected in tissues from uninfected animals or in non-target tissues of leukemic animals infected at birth. The results are consistent with the working hypothesis that the virus was integrated in all cells of the animal, possibly including the germ line. Fifty to 100 times more M-MuLV-specific RNA was detected in tumor tissues than was found in non-target organs such as liver, brain, and testes. Since all organs contained the same amount of virus-specific DNA, these results indicate that the M-MuLV-specific DNA can be differentially expressed in different tissues.

Direct transformation of rodent fibroblasts by jaagsiekte sheep retrovirus DNA

Jaagsiekte sheep retrovirus (JSRV) is the causative agent of ovine pulmonary carcinoma, a unique animal model for human bronchioalveolar carcinoma. We previously isolated a JSRV proviral clone and showed that it was both infectious and oncogenic. Thus JSRV is necessary and sufficient for the development of ovine pulmonary carcinoma, but no data are available on the mechanisms of transformation. Inspection of the JSRV genome reveals standard retroviral genes, but no evidence for a viral oncogene. However, an alternate ORF in pol (orf-x) might be a candidate for a transforming gene. We tested whether the JSRV genome might encode a transforming gene by transfecting an expression plasmid for JSRV [pCMVJS21, driven by the cytomegalovirus (CMV) immediate early promoter] into mouse NIH 3T3 cells. Foci of transformed cells appeared in the transfected cultures 2-3 weeks posttransfection; cloned transformants showed anchorage independence for growth, and they expressed JSRV RNA. These results indicate that the JRSV genome contains information with direct transforming potential for NIH 3T3 cells. Transfection of a mutated version of pCMVJS21 in which the orf-x protein was terminated by two stop codons also gave transformed foci. Thus, orf-x was eliminated as the candidate transforming gene. In addition, another derivative of pCMVJS21 (pCMVJS21DeltaGP) in which the gag, pol (and orf-x) coding sequences were deleted also gave transformed foci. These results indicate that the envelope gene carries the transforming potential. This is an unusual example of a native retroviral structural protein with transformation potential.

Retrovirus-induced ovine pulmonary adenocarcinoma, an animal model for lung cancer

Studies on the molecular mechanisms of transformation of retrovirus-induced neoplasms in domestic and laboratory animal species have provided insights into the genetic basis of cancer. Ovine pulmonary adenocarcinoma (OPA) is a retrovirus-induced spontaneous lung tumor of sheep that has striking analogies to some forms of human adenocarcinoma. The etiologic agent of OPA, jaagsiekte sheep retrovirus (JSRV), is unique among retroviruses for having a specific tropism for the differentiated epithelial cells of the lung, and it is the only virus known to cause a naturally occurring lung adenocarcinoma. Expression of the JSRV envelope protein is sufficient to induce cell transformation in vitro, possibly via the activation of the phosphatidylinositol 3-kinase/Akt-signaling pathway mediated by the cytoplasmic tail of the transmembrane protein. The aim of this review is to draw the attention of basic and clinical scientists engaged in lung cancer research to this unique animal model, to explore the possible use of OPA as a tool to investigate the mechanisms of pulmonary carcinogenesis, and to underline the similarities between OPA and some forms of human lung adenocarcinoma. The possibility of a viral etiology for the latter will be evaluated in this review.

A 7-day activity diary for assessment of daily energy expenditure validated by the doubly labelled water method in adolescents

OBJECTIVES

To validate the use of an activity diary and predicted BMR for assessment of daily total energy expenditure (TEE) and physical activity level (PAL = TEE/BMR) in adolescents.

DESIGN

TEE and PAL estimated from activity diary records kept for seven days and BMR predicted from age, gender and body weight were compared with the results of doubly labelled water (DLW) measurements and indirect calorimetry performed during the same time period.

SETTING

The Unit of paediatric Physiology of the Department of Clinical Physiology, University Hospital, Uppsala, Sweden.

SUBJECTS

Fifty randomly selected 15 y old adolescents (25 boys and 25 girls).

RESULTS

The mean difference between TEE estimated in all adolescents by the activity diary and by DLW methods was 1.2%. The limits of agreement (mean difference 2 s.d.) were -3.47 and 3.77 MD/d, equivalent to a coefficient of variation of 15%. The mean difference between PAL assessed by activity diary records and by DLW measurements was 0.001, and the limits of agreement between the two methods were 0.54.

CONCLUSIONS

The results imply that the activity diary method provides a close estimate of TEE and PAL in population groups.

Elastocapillary self-assembled neurotassels for stable neural activity recordings

Implantable neural probes that are mechanically compliant with brain tissue offer important opportunities for stable neural interfaces in both basic neuroscience and clinical applications. Here, we developed a Neurotassel consisting of an array of flexible and high-aspect ratio microelectrode filaments. A Neurotassel can spontaneously assemble into a thin and implantable fiber through elastocapillary interactions when withdrawn from a molten, tissue-dissolvable polymer. Chronically implanted Neurotassels elicited minimal neuronal cell loss in the brain and enabled stable activity recordings of the same population of neurons in mice learning to perform a task. Moreover, Neurotassels can be readily scaled up to 1024 microelectrode filaments, each with a neurite-scale cross-sectional footprint of 3 × 1.5 μm², to form implantable fibers with a total diameter of ~100 μm. With their ultrasmall sizes, high flexibility, and scalability, Neurotassels offer a new approach for stable neural activity recording and neuroprosthetics.

gag-Related polyproteins of Moloney murine leukemia virus: evidence for independent synthesis of glycosylated and unglycosylated forms

Immunoprecipitation of labeled extracts from murine leukemia virus-infected cells with antisera specific for internal structural (gag) proteins yields three major gag-related polyproteins with molecular weights of 180,000 (Pr180gag-pol), 80,000, and 65,000 (Pr65gag). It has been shown by others that Pr65gag is the immediate precursor of the internal structural (gag) protein, and that Pr180gag-pol is the precursor to reverse transcriptase. In studies reported here, the 80,000-dalton gag-related polyprotein from Moloney strain murine leukemia virus (M-MuLV)-infected cells was found to be glycosylated by the following criteria: (i) incorporation of [3H]mannose, (ii) a change in electrophoretic mobility upon digestion with endoglycosidase H, and (iii) a change in electrophoretic mobility when glycosylation was inhibited by treatment of the cells with tunicamycin during labeling. The 80,000-dalton gag polyprotein has therefore been designated GpP80gag. The unglycosylated form of GpP80gag was a polypeptide of 75,000 daltons. A comparison of [3H]mannose and [3H]galactose labeling experiments suggested that GpP80gag is further glycosylated to yield a glycopolypeptide of 95,000 daltons. This 95,000-dalton polypeptide is relatively rapidly cleaved to yield two glycopeptides of 55,000 and 40,000 daltons which are released into the cell culture fluid, as soluble proteins. Cell-free translation of M-MuLV genomic RNA resulted in two major gag-related products of 75,000 and 65,000 daltons. The 65,000-dalton gag-related cell-free translation product comigrated with Pr65gag, and the 75,000-dalton cell-free product comigrated with the unglycosylated form of GpP80gag. Both of the gag-related cell-free translation products could be labeled with [35S]formyl methionine, which is incorporated only as the N-terminal amino acid during translation. Other investigators have shown that GpP80gag and Pr65gag differ at their N-termini, and these results combined with those reported here suggest that GpP80gag and Pr65gag are translated from two separate initiation sites in M-MuLV RNA.