The Pem homeobox gene: rapid evolution of the homeodomain, X chromosomal localization, and expression in reproductive tissue

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Title: The Pem homeobox gene: rapid evolution of the homeodomain, X chromosomal localization, and expression in reproductive tissue
Author: Maiti, Sourindra; Doskow, Jessica; Sutton, Keith; Nhim, Ronald; Lawlor, David; Leyan, Karin; Lindsey, J.; Wilkinson, Miles
Abstract: A hallmark of homeobox genes is their high degree of sequence conservation in distantly related species. Here, we report the chromosomal localization, sequence, and expression pattern of an orphan homeobox gene,Pem,that encodes a homeodomain (HD) that has undergone a surprisingly high rate of evolutionary change. The N-terminal portion of thePemHD, which includes the first two α-helices, exhibits only 44% sequence identity between ratPem(r.Pem) and mousePem(m.Pem). This N-terminal subdomain exhibited an extremely high frequency of nonsynonymous substitutions, severalfold higher than other regions of thePemprotein. In contrast, the third helix, which is known to confer most of the base-specific contacts of HDs with DNA, was almost identical inr.Pemandm.Pem.Several lines of evidence suggested that the rat and mouse genes that we identified asPemgenes are true homologues: (1) ther.Pemandm.Pemgenes both reside on the X chromosome; (2) they possess identical exon/intron splice junctions; (3) they both encode a distinctive motif upstream of the HD that is unique toPem;and (4) the onlym.Pem-like gene we were able to identify in the rat genome other thanr.Pemwas a pseudogene,r.Pem-ps,whose sequence and chromosomal localization indicated that it was derived by reverse transcription and reinsertion into the genome. The functionalr.Pemgene is selectively expressed in placenta, testis, epididymis, and ovary. This expression pattern is of interest since other genes transcribed in reproductive tissue have also been shown to undergo high rates of sequence divergence. The high rate of amino acid substitutions in the N-terminal region of thePemHD suggests the possibility of species-specific directional selection.
Record URI: http://hdl.handle.net/1850/2411
Publishers URL: http://dx.doi.org/10.1006/geno.1996.0291
Date: 1996-06-15

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