Open AccessRNA-mediated gene duplication: the rat preproinsulin I gene is a functional retroposon.
Author(s) -
Marcelo B. Soares,
Eric A. Schon,
A Henderson,
S K Karathanasis,
R Cate,
Scott Zeitlin,
John M. Chirgwin,
Argiris Efstratiadis
Publication year - 1985
Publication title -
molecular and cellular biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.14
H-Index - 327
eISSN - 1067-8824
pISSN - 0270-7306
DOI - 10.1128/mcb.5.8.2090
Subject(s) - biology , gene , intron , genetics , gene duplication , retroposon , concerted evolution , retrotransposon , gene cluster , gene family , gene conversion , pseudogene , microbiology and biotechnology , transposable element , gene expression , genome
Rats and mice have two, equally expressed, nonallelic genes encoding preproinsulin (genes I and II). Cytological hybridization with metaphase chromosomes indicated that both genes reside on rat chromosome I but are approximately 100,000 kilobases apart. In mice the two genes reside on two different chromosomes. DNA sequence comparisons of the gene-flanking regions in rats and mice indicated that the preproinsulin gene I has lost one of the two introns present in gene II, is flanked by a long (41-base) direct repeat, and has a remnant of a polydeoxyadenylate acid tract preceding the downstream direct repeat. These structural features indicated that gene I was generated by an RNA-mediated duplication-transposition event involving a transcript of gene II which was initiated upstream from the normal capping site. Sequence divergence analysis indicated that the pair of the original gene and its retroposed, but functional, counterpart (which appeared about 35 million years ago) is maintained by strong negative selection operating primarily on the segments encoding the chains of the mature hormone, whereas the segments encoding the parts of the polypeptide that are eliminated during processing and also the introns and the flanking regions are evolving neutrally.