RESUMO
The gene encoding the carcinoma-associated antigen defined by the monoclonal antibody GA733 is a member of a family of at least two type I membrane proteins. This study describes the mechanism of evolution of the GA733-1 and GA733-2 genes. A full-length cDNA clone for GA733-1 was obtained by screening a human placental library with a genomic DNA probe. Comparative analysis of the cDNA sequence with the previously determined genomic sequence confirmed that GA733-1 is an intronless gene. The GA733-2 gene encoding the monoclonal antibody-defined antigen was molecularly cloned with a cDNA probe and partially sequenced. Comparison of GA733-2 gene sequences with the previously established cDNA sequence revealed that this gene consists of nine exons. The putative promoter regions of the GA733-1 and GA733-2 genes are unrelated. These findings suggest that the GA733-1 gene was formed by the retroposition of the GA733-2 gene via an mRNA intermediate. Prior to retroposition, the GA733-2 gene had been affected by exon shuffling. Analysis of GA733-2 exons revealed that many delineate structural motifs. The GA733-1 retroposon was localized either to chromosome region 1p32-1p31 or to 1p13-1q12, and the GA733-2 founder gene was localized to chromosome 4q.
Assuntos
Antígenos Glicosídicos Associados a Tumores/genética , Evolução Biológica , Elementos de DNA Transponíveis/genética , Sequência de Aminoácidos , Sequência de Bases , Mapeamento Cromossômico , Cromossomos Humanos Par 1 , Cromossomos Humanos Par 4 , Clonagem Molecular , Genoma Humano , Humanos , Dados de Sequência Molecular , Família Multigênica , RNA Mensageiro/biossíntese , Análise de Sequência de DNA , Homologia de Sequência de AminoácidosRESUMO
The ME1a1 and ME1a2 elements are cis-acting DNA sequences that exist at positions -46 and -85, respectively, within the P2 promoter of the c-myc gene. These elements are required for optimal transcription initiation from P2. The proteins that bind to these elements are identical or very similar. Here we have isolated a cDNA clone that encodes the carboxy-terminal 494 amino acids of the human ME1a1/ME1a2 factor. This factor is referred to as "ZF87" (zinc-finger protein, 87 kilodaltons). ZF87 specifically binds the ME1a1 element with higher affinity than the ME1a2 element. Western blot analysis indicates that the full-length protein has a relative molecular mass of approximately 87,000 daltons, and Northern blot analysis shows that it is encoded by a 5-kb transcript. ZF87 contains six zinc-finger domains, of the Cys2-His2 type, at the carboxy terminus of the protein. The protein also contains extended tracts of polyalanine.
Assuntos
DNA/isolamento & purificação , Genes myc , Regiões Promotoras Genéticas , Dedos de Zinco/genética , Sequência de Aminoácidos , Sequência de Bases , Sítios de Ligação , Northern Blotting , Western Blotting , DNA/química , DNA/metabolismo , Humanos , Dados de Sequência Molecular , Peso Molecular , Sequências Repetitivas de Ácido NucleicoRESUMO
The monoclonal antibody-defined, tumor-associated antigen GA733 was purified from the SW948 human colorectal carcinoma cell line and its partial amino acid sequence was determined. By using a synthetic oligonucleotide probe, two recombinants were isolated from a total human genomic library. We prove the existence of a family of GA733 genes. One of the genomic isolates is demonstrated to be an intronless gene, which is transcribed in pancreatic carcinoma cell lines and in placenta. The GA733 proteins were observed to contain sequences homologous to a repeat unit occurring 10 times in thyroglobulin and once in the HLA-DR-associated invariant chain. A more evolutionarily distant relationship was found with the alpha chain of the interleukin 2 growth factor receptor.
