We sequenced the envelope (env) gene and 3' long terminal repeat of a Friend mink cell focus-inducing virus (F-MCFV). We also sequenced the gp7O coding regions for two cDNA clones of another F-MCFV. The deduced amino acid sequence of the env gene products of both F-MCFVs were compared to the corresponding sequences of other MCFVs and of ecotropic viruses. The env polypeptides of the different viruses showed long stretches of homology in the carboxy-terminal half of gp7O and in p15env ("constant region"). The amino-terminal half of gp7O was very similar in all MCFVs, but showed extensive variations relative to the ecotropic viruses ("differential region"). This differential region in all MCFVs is of endogeneous origin. We show evidence that this region carries determinants for ecotropic or polytropic host range. No indication could be found that the env gene products determine the histological type of disease caused by particular MCFVs. When the long terminal repeats of F-MCFV and Friend murine leukemia virus were compared with those of other viruses causing either lymphatic leukemia or erythroleukemia, several nucleotides were localized which might determine the histological type of disease caused by these viruses.

Viral interference studies have demonstrated the existence of four distinct murine leukemia virus (MuLV) receptors on NIH 3T3 mouse cells. The four viral interference groups are ecotropic MuLV; mink cell focus inducing virus (MCF); amphotropic MuLV; and 1OA1, a recombinant derivative of amphotropic MuLV that uses a unique receptor but also retains affinity for the amphotropic MuLV receptor. We report here that 1OAl infects rat and hamster cells, unlike its amphotropic parent. We isolated an infectious molecular clone of 1OAl and present here the sequences of the env genes and enhancer regions of amphotropic MuLV and 1OAl. The deduced amino acid sequences of amphotropic MuLV and 1OAl gp70Su are remarkably similar to those of MCF and xenotropic MuLV (for which mouse cells lack receptors), with 64% amino acids identical in the four groups. We generated a consensus from these comparisons. Further, the differences are largely localized to a few discrete regions: (i) amphotropic MuLV has two short insertions relative to MCF, at residues 87 to 92 and 163 to 169, and (ii) amphotropic MuLV and MCF are totally different in a hypervariable region, which is >30% proline, at residues-253 to 304. 1OAl closely resembles amphotropic MuLV in its N terminus but contains an MCF-type hypervariable region. These results suggest the possibility that receptor specificity is localized in these short variable regions and further that the unique receptor specificity of 1OAl is due to the novel combination of amphotropic MuLV and MCF sequences rather than to the presence of any novel sequences. The Env proteins of ecotropic MuLVs are far more distantly related to those of the other four groups than the latter are to each other. We also found that the enhancer regions of amphotropic MuLV and 1OAl are nearly identical, although 1OAl is far more leukemogenic than amphotropic MuLV.

The envelope gene of the helper-independent, highly leukemogenic virus Friend murine leukemia virus was sequenced by using a molecular clone of a Friend murine leukemia provirus. The deduced amino acid sequences of the envelope proteins gp70 and p15env were homologous to the sequences of Moloney murine leukemia virus (86%) and Akv (76%). However, a stretch of about 40 amino acid residues near the middle of gp70 was dissimilar in Friend and Moloney murine leukemia viruses and Akv. In this type-specific region the gp70s of all three viruses contained more than 30% proline residues, giving this sequence a very rigid conformation. We suggest that this rigid and highly variable region of gp70 participates in infection by recognition of cell surface receptors and, in addition, might contribute to the different oncogenic spectra of murine leukemia viruses.

For the isolation of cDNA clones encoding the carcinoembryonic antigen (CEA), we have constructed a cDNA library from human colon tumor mRNA. The library was screened with various oligonucleotides whose sequence had been deduced from partial amino acid sequence data for CEA. Positive candidate clones were hybridized with a probe for repetitive DNA, because CEA mRNA contains anAlu repetitive element, and with a fragment of a genomic clone of nonspecific cross-reacting antigen, an antigen closely related to CEA. Here we report the nucleotide sequence of the two overlapping CEA cDNA clones comprising 1422 nucleotides of CEA mRNA. This sequence encodes the 372 COOH-terminal amino acids of CEA followed by 305 nucleotides of 3' untranslated sequence containing a truncated Alu repeat. The predicted protein sequence is composed of two repeats comprising 178 amino acids, each with an exceptionally high homology of 67%. Each repeat unit contains four conserved cysteine residues and six to nine putative N-glycosylation sites. CEA mRNA is most strongly expressed in primary colon tumors and, to a lesser extent, in normal colonic tissue. No CEA mRNA is found in HeLa cells and normal human fibroblasts.

Transcription of DNA from the RNA genome of avian sarcoma virus by IRNA-directed DNA polymerase in vitro initiates on a primer (tRNATrP) located near the 5'-terminus of the viral genome. One of the major products of transcription is a single-stranded DNA chain complementary to a sequence of 101 nucleotides immediately distal to the site of initiation of DNA synthesis. We have determined the complete nucleotide sequence of this transcribed chain for the Prague strain of avian sarcoma virus, a partial sequence of the transcribed chain for the Bratislava 77 strain of avian sarcoma virus, and the sequence of a DNA transcript that is shorter than the transcribed singlestranded chain. Our data define the location of tRNATrP on the genome of avian sarcoma virus and provide the sequence of 119 nucleotides at the 5'-terminus of the genome. Portions of this sequence may be involved in the binding of RNA-directed DNA polymerase, the initiation of translation from viral messenger RNA, the extension of RNA-directed DNA synthesis from the 5'-to the 3'-terminus of viral RNA, and the integration of viral DNA into the host genome.Avian sarcoma viruses (ASV) are retroviruses (1) whose replication requires transcription of DNA from the viral genome by RNA-directed DNA polymerase (2). Transcription from the genome of ASV in vitro initiates on the primer tRNATrP (3, 4) located near the 5'-terminus of the viral RNA (5, 6). One of the major products of transcription is a DNA chain (denoted cDNA,5) complementary to 101 nucleotides of the viral RNA immediately distal to the site of initiation (7-9). We have previously purified and characterized cDNA5' for ASV and we have described the utility of this DNA for the analysis of viral structure and replication (10). We report here the complete sequence of the 101 nucleotides which constitute cDNA5' synthesized with the Prague subgroup C strain (Pr-C) of ASV and a partial sequence for cDNA5' of Bratislava 77 subgroup C strain (B77-C) of ASV.Using the nucleotide sequence of cDNA5' and previous data from our laboratory, we have deduced the sequence of 119 nucleotides at the 5'-terminus of the Pr-C ASV genome. The details of this sequence and its secondary structure are of interest because the 5'-terminus of the viral genome is involved in the initiation of DNA synthesis (7,11,12), the binding of ribosomes for the initiation of viral protein synthesis (13,14), the extension of RNA-directed DNA synthesis from the 5'-terminus to the 3'-terminus of the viral genome (7,11,12), and the integration of viral DNA into the host genome (7,11,12 Cells and Viruses. We have described previously the propagation and purification of ASV (17). B77-C ASV was obtained from R. Friis. Pr-C ASV was provided as concentrated suspensions by University Laboratories through the auspices of the Office of Program Resources and Logistics, National Cancer Institute. Both strains of virus have been extensively propagated and cannot be considered clonal stocks.Isolation of cDNA51. The synthesis and purification of cDNAs...