Nucleotide sequence of cDNA clones of the murine myb proto-oncogene

We have isolated cDNA clones of murine c-myb mRNA which contain approximately 2.8 kb of the 3.9-kb mRNA sequence. Nucleotide sequencing has shown that these clones extend both 5' and 3' to sequences homologous to the v-myb oncogenes of avian myeloblastosis virus and avian leukemia virus E26. The sequence contains an open reading frame of 1944 nucleotides, and could encode a protein which is both highly homologous, and of similar size (71 kd), to the chicken c-myb protein. Examination of the deduced amino acid sequence of the murine c-myb protein revealed the presence of a 3-fold tandem repeat of 52 residues near the N terminus of the protein, and has enabled prediction of some of the likely structural features of the protein. These include a high alpha-helix content, a basic region toward the N terminus of the protein and an overall globular configuration. The arrangement of genomic c-myb sequences, detected using the cDNA clones as probes, was compared with the reported structure of rearranged c-myb in certain tumour cells. This comparison suggested that the rearranged c-myb gene may encode a protein which, like the v-myb protein, lacks the N-terminal region of c-myb.

Structure and expression of the mRNA for murine granulocyte-macrophage colony stimulating factor

A cDNA containing a virtually complete copy of the mRNA for the haemopoietic growth regulator, granulocyte-macrophage colony stimulating factor (GM-CSF), has been isolated from a murine T lymphocyte cDNA library. When a eukaryotic expression vector with this cDNA coupled to the SV40 late promoter was introduced into simian COS cells, significant quantities of GM-CSF were secreted. Since all of the biological activities previously ascribed to highly purified GM-CSF were exhibited in the COS cell-derived GM-CSF, all of these activities are intrinsic to the product of a single gene. There are two potential translational initiation codons in the GM-CSF mRNA; the first is buried in the stem and the second located in the loop of a very stable hairpin structure. Expression studies using deletion derivatives of the cDNA indicated that the second AUG is able to initiate the translation and secretion of GM-CSF. The amino acid sequence of the leader peptide is rather atypical for a secreted protein and we speculate that molecules which initiate at the first AUG might exist as integral membrane proteins whereas those initiating at the second are secreted.

Disruption of learned and spontaneous alternation in the rat by trimethyltin: chronic effects

Trimethyltin (TMT) is a known neurotoxin which produces behavioral anomalies including hyperactivity, aggressiveness, perseveration, and learning deficits. These dysfunctions appear to be related to a severe loss of neurons in the hippocampal formation of the TMT-treated rat. In order to assess the effect of TMT exposure upon spontaneous and learned alternation, male Long-Evans rats were pretested for reinforced spontaneous alternation and then treated with either 7 mg/kg of TMT [( CH3]3SnCl) or the 0.9% NaCl vehicle. After treatment these groups were further subdivided and half of each group was tested in a "T" maze for reinforced spontaneous alternation while the remainder was tested for learned alternation. The TMT-treated rats uniformly ran faster on the second choice of reinforced spontaneous alternation tests than did controls. In addition, the TMT-treated rats made fewer alternations than controls, regardless of whether or not only successful alternations were being reinforced. These results are discussed in light of the known neurobehavioral consequences of TMT exposure.

Molecular cloning of cDNA encoding a murine haematopoietic growth regulator, granulocyte-macrophage colony stimulating factor

DNA clones specifying the murine granulocyte-macrophage colony stimulating factor have been isolated. This haematopoietic growth factor is encoded by a unique gene specifying a messenger RNA of 1,200 nucleotides and a polypeptide of 118 amino acids. It bears no structural similarity to the functionally related factor, interleukin-3, described recently.

Murine T lymphomas in which the cellular myc oncogene has been activated by retroviral insertion

The myc oncogene is implicated here in T lymphocyte neoplasia. Cloning revealed a retroviral insert 0.7-1.3 kb 5' to c-myc in two T lymphomas induced by Soule murine leukemia virus and in a spontaneous T lymphoma ( Tikaut ) of an AKR mouse, a strain in which leukemogenesis involves recombinant retroviruses (MCF viruses). The tumor c-myc mRNAs appear normal but their level is approximately 5-fold higher than in most T lymphomas lacking c-myc rearrangement. Since each insert would be transcribed away from c-myc, its activation cannot involve the promoter of the long terminal repeat (LTR) but could reflect an enhancer, like that demonstrated within the Soule LTR. The Tikaut provirus has an MCF-like recombinant env gene and LTR sequence. MCF-like inserts were found near c-myc in seven of 31 other AKR T lymphomas; two lie 3' to c-myc and the five upstream are oriented away from c-myc. We conclude that a quarter of retrovirus-induced T lymphomas involve activation of c-myc, probably via the LTR enhancer.

Adenovirus type 12-transformed rat embryo brain and rat liver epithelial cell lines: adenovirus type 12 genome content and viral protein expression

By Southern blotting analysis, six adenovirus type 12 (Ad-12)-transformed rat embryo brain cell lines and one Ad-12-transformed rat liver epithelial line were shown to contain all or nearly all the Ad-12 genome. Another Ad-12 rat liver epithelial cell line contained a repeating structure consisting of only the left-hand 16% of the Ad-12 genome. Three Ad-12-specified proteins (molecular weights, 52,000, 41,000, and 18,000) were found by immunoprecipitation to be common to all of these cell lines. Two rat liver epithelial lines, produced from an Ad-12-infected culture and previously shown to be T-antigen negative by immunofluorescence, contained no detectable Ad-12 genome or Ad-12-specified proteins. Although some of the rat embryo brain transformants had been shown previously to express "late" Ad-12 mRNA, no Ad-12 structural proteins were found to be produced by these cell lines.

Nucleotide sequence analysis of the leader segments in a cloned copy of adenovirus 2 fiber mRNA

Fiber mRNA of adenovirus 2 has been used as a template for RNA-dependent DNA polymerase. The resulting cDNA/RNA hybrids have been inserted at the Pst I site of the plasmid vector pBR322 after A:T tailing. One recombinant plasmid, pJAW 43, has been characterized in detail and shown to contain sequences from the main body of fiber mRNA, the three leaders common to most late adenoviral mRNAs and a fourth leader found in some species of fiber mRNA. The complete DNA sequence of the leader region has been determined and does not contain the initiation codon AUG, although this codon does occur immediately downstream from the junction between the fourth leader and the main body of the fiber mRNA. The first leader (map coordinate 16.6) is 41 nucleotides long, the second (from 19.6) is 71 nucleotides, the third (from 26.6) is 88 nucleotides and the fourth (from 78.5) is 181 nucleotides. The location of junctions between viral leaders and intervening sequences has been determined by reference, where possible, to sequences of the adenovirus 2 genome. Although the presence of short repeated sequences at the boundaries of intervening sequences and leaders makes it impossible to locate the splice point unambiguously, all of the leader-intervening sequence junctions can be arranged to stress a common feature--the presence of the dinucleotides GT and AG at the 5' and 3' ends, respectively, of the intervening sequences. This prototype sequence, which has also been recognized at or near the splice points in other eucaryotic systems, is possibly part of a larger unit which serves as a recognition site for specific excision-ligation events that ultimately lead to the production of mature mRNAs.

A novel method to map transcripts: evidence for homology between an adenovirus mRNA and discrete multiple regions of the viral genome

A method has been devised which permits mapping of transcripts by a two-step hybridization procedure (sandwich hybridization). RNA extracted from cells infected with an adenovirus-SV40 hybrid (Ad2+ND1) was hybridized to restriction endonuclease fragments of adenovirus type 2 (Ad2) DNA immobilized on nitrocellulose filters. RNAs containing both Ad2 and SV40 sequences formed duplexes through their Ad2 sequences, leaving their SV40 sequences as protruding tails. Annealing with 32P-labeled SV40 DNA caused these tails to become labeled, permitting autoradiographic identification of the sequences of Ad2 DNA which are homologous to the RNA. The high sensitivity of this technique, achieved through the use of 32P-labeled RNA of high specific activity, has led to the observation that hybridization of Ad2+ND1 RNA occurs at several locations on the Ad2 genome, in addition to the expected sites of hybridization proximal to the SV40 insertion.