Shen / Oral

Genomic evolution of primates

C.-K. James Shen, Institute of Molecular Biology Academia Sinica, Nankang, Taipei, Taiwan 11529, Republic of China

     Many labs have studied the evolution of primates by sequence and expression analyses of specific genomic loci. In the case of the adult globin region, the analysis has revealed promiscuously high rate of nucleotide substitutions at the replacement sites of the baboon a globin genes. While the two duplicated units containing the adult a 2/a 1 globin genes have undergone efficient gene correction, numberous DNA insertion and genomic rearrangement events have occurred. Interestingly, the latter two processes are tightly coupled, suggesting the existence of hot spots of DNA recombination at specific sequence motifs, and/or chromatin structures.
     More recently, we have discovered that in somatic cells, the human DNA (5-cytosine)-methyltransferase gene, Dnmt1, encodes two alternatively spliced forms of enzyme, instead of one as previously thought. The 48 bp extra exon in one of these isoforms is actually derived from an Alu family repeat. The same scheme is also utilized in chimpanzee. Furthermore, the mouse Dnmt1 gene also encodes two mRNAs differing by 3 nt at the same position as the primate Dnmt 1 transcripts. However, no such alternative splicing occurs in the somatic cells of the Old World Monkeys. The possible implications of these observations are discussed in relation to the functions of the enzymes and to the primate evolution.

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