The retroviral transmembrane envelope protein p15E is immunosuppressive in that it inhibits immune responses of lymphocytes, monocytes, and macrophages. A region of p15E has been conserved among murine and feline retroviruses; a homologous region is also found in the transmembrane envelope proteins of the human retroviruses HTLV-I and HTLV-II and in a putative envelope protein encoded by an endogenous C-type human retroviral DNA. A peptide (CKS-17) was synthesized to correspond to this region of homology and was examined for its effects on lymphocyte proliferation. CKS-17 inhibited the proliferation of an interleukin-2-dependent murine cytotoxic T-cell line as well as alloantigen-stimulated proliferation of murine and human lymphocytes. Four other peptides, representing different regions of virus proteins, were inactive. These results suggest that the immunosuppressive portion of retroviral transmembrane envelope proteins may reside, at least in part, in a-conserved sequence represented by the CKS-17 peptide.

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We propose a revised standardized nomenclature for the proteins common to all retroviruses on the basis of biological function, enzymatic activity, and/or virion location data. (We do not discuss proteins specific for subfamilies or only some retroviruses.

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Harvey murine sarcoma virus is a retrovirus which transforms cells by means of a single virally encoded protein called p21 has. We have determined the nucleotide sequence of 1.0 kilobase in the 5' half of the viral genome which encompasses the has coding sequences and its associated regulatory signals. The nucleotide sequence has identified the amino acid sequence of two additional overlapping polypeptides which share their reading frames and the carboxyl termini with p21 but which contain additional NH2-terminal amino acids.

The proteins encoded by the human TPR-MET oncogene (p65tPr-mt) and the human MET protooncogene (p140O"') have been identified. The p65tPr-met and p44lt, as well as a truncated TPR-MET product expressed in Escherichia coli, p509et, are autophosphorylated in vitro on tyrosine residues. Using the immunocomplex kinase assay, p1404et activity was detected in various human tumor epithelial cell lines. In vivo, p65P'-pr-is phosphorylated on both serine and tyrosine residues, while pl4Ont is phosphorylated on serine and threonine. pl4et is labeled by cell-surface iodination procedures, suggesting that it is a receptor-like transmembrane proteintyrosine kinase.The MET oncogene was identified in a N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-treated human osteogenic sarcoma cell line, MNNG-HOS (1, 2), by using the murine NIH 3T3 cell transfection assay. We have shown that activation of the MET oncogene occurred via a chromosomal DNA rearrangement (3,4). This rearrangement created a hybrid TPR-MET gene with upstream sequences derived from a locus on chromosome 1 (designated TPR for translocated promoter region) fused to downstream sequences from the MET protooncogene locus located on chromosome 7, 7q21-31 (5). The MET protooncogene is predominantly expressed in human fibroblast and epithelial cell lines as a 9.0-kilobase (kb) RNA species, whereas the activated TPR-MET oncogene expresses a novel 5.0-kb TPR-MET hybrid RNA species (3). Nucleotide sequence analysis of the MET protooncogene cDNA revealed an open reading frame of 1408 amino acids with features characteristic of the growth factor receptor protein-tyrosine kinase family (6). The predicted primary structure contains a 926-amino acid external domain and a 435-amino acid cytoplasmic domain with homology to the protein-tyrosine kinase family of genes. We have used C-terminal anti-MET peptide antibodies to identify and characterize the TPR-MET oncogene and MET protooncogene protein products. Both p65tPr-met and p140met are protein-tyrosine kinases and undergo autophosphorylation in vitro. Expression of the MET Kinase Domain in Escherichia coli. The plasmid pBR5a, containing 2.1-kb TPR-MET human cDNA (6) was digested with HindIlI, and the resulting 1.6-kb cDNA fragment containing the MET kinase domain was inserted in frame at the unique HindIII site of pJLA16 (7) to generate plasmid pAMET-2. A 50-kDa protein (p5soe,) was expressed in bacterial cells containing pAMET-2 upon induction at 420C. The p5Oet was purified as described (7) and analyzed by NaDodSO4/polyacrylamide gel electrophoresis followed by staining with Coomassie blue or assayed in vitro for kinase activity. MATERIALS AND METHODSPreparation of MET-Specific Antisera. Three peptides corresponding to the predicted 8-, 16-, and 28-amino acids at the C terminus of the MET protein (5) were constructed by solid-phase Merrifield procedures (8) as described (9). Peptide coupled to keyhole limpet hemocyanin (9, 10) was mixed with Freund's complete adjuvant and administered subcutaneously into rabbits. Sera were...

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The possibility of whether tRNAs with and without a highly modified base in their anticodon loop may influence the level of retroviral ribosomal frameshifting was examined. Rabbit reticulocyte lysates were programmed with mRNA encoding UUU or AAC at the frameshift site and the corresponding Phe tRNA with or without the highly modified wyebutoxine (Y) base on the 3' side of its anticodon or Asn tRNA with or without the highly modified queuine (Q) base in the wobble position of its anticodon added. Phe and Asn tRNAs without the Y or Q base, respectively, stimulated the level of frameshifting, suggesting that the frameshift event is influenced by tRNA modification status. In addition, when AAU occurred immediately upstream of UUU as the penultimate frameshift site codon, addition of tRNAAsn without the Q base reduced the stimulatory effect of tRNAPhe without the Y base, whereas addition of tRNAAsn with the Q base did not alter the stimulatory effect. The addition of tRNAAsn without the Q base and tRNAPhe with the Y base inhibited frameshifting. The latter studies suggest an interplay between the tRNAs decoded at the penulimate frameshift and frameshift site codons that is also influenced by tRNA modification status. These data may be intrepreted as indicating that a hypomodified isoacceptor modulates frameshifting in an upward manner when utilized at the frameshift site codon, but modulates frameshifting in a downward manner when utilized at the penultimate frameshift site codon.