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  • Sulfo-NHS-SS-Biotin The haspin gene is also

    2021-11-29

    The haspin gene is also unusual because it lacks introns. This is more remarkable when one compares the mammalian genes to those of likely haspin orthologs that are present in the genomic sequences of other species. Such genes in Drosophilamelagonaster, Arabidopsisthaliana and Caenorhabditiselegans all contain introns within their kinase encoding regions (data not shown). The location of some of these introns is precisely conserved in Drosophila and Arabidopsis. This suggests that these introns were acquired before divergence of the plant and insect lineages, but that they have since been lost from mammals, probably before the divergence of humans and mice. One mechanism by which genes may lose introns is by retro-insertion of processed mRNAs into the genome. This process normally yields processed pseudo genes since it is unlikely that a retro-insertion event will provide a suitable promoter to drive gene expression. Notable exceptions include the human autosomal testis-specific genes for phosphoglycerate kinase, PGK-2, and pyruvate dehydrogenase E1α, PDHA2. Both of these genes are functional intronless genes thought to be derived from intron-containing parent genes on the X chromosome (McCarrey and Thomas, 1987, Dahl et al., 1990). The location of the haspin gene, and its lack of introns, may be due to a similar retro-insertion into an intron of the αE gene. Consistent with this proposal is the presence of the possible remnants of a poly(A) tract in the 3′ region of both human and murine haspin genes that may be derived from the poly(A) tail of the inserted mRNA (see Fig. 8B). The insertion probably occurred into a pre-existing intron because intron 26 of αE is in the same position and phase as equivalent introns in other integrin genes. It is striking that haspin, PGK-2 and PDHA2 are all expressed principally in postmeiotic spermatogenic cells. Since haploid Sulfo-NHS-SS-Biotin contain only one copy of each chromosome, it has been suggested that the necessity to maintain expression of genes on the X chromosome after X-inactivation in germ cells is responsible for the evolutionary maintenance of the retrogenes for PGK-2 and PDHA2 (McCarrey and Thomas, 1987, Dahl et al., 1990). Alternatively, since retro-insertion events must occur in the germline in order to be inherited, it follows that the parent gene must be transcribed there, and it is also likely that retro-insertion events into chromosomal loci that are active in germ cells will be favored. Therefore, a preponderance of housekeeping retrogenes and retrogenes that are strongly expressed in the testis might be expected. As predicted by this hypothesis, not all retrogenes seem to originate from the X chromosome. For example the intron-containing mouse S-adenosylmethionine decarboxylase gene Amd1, the parent of the likely retrogene Amd2 (Persson et al., 1995), is on chromosome 10. A candidate parent gene with homology to haspin could not be identified upon searching the human gene sequence database. It is possible that the original gene has been lost since creation of the haspin retrogene, or that it remains to be sequenced. Cloning of the human haspin cDNA revealed that the derived human haspin protein sequence is 83% identical to murine haspin in the C-terminal kinase domain, but only 53% identical in the N-terminal region. Database searches with the C-terminal haspin kinase domain reveal that likely haspin orthologs with 34–39% identity to human haspin are found in Schizosaccharomycespombe, A.thaliana, C.elegans and D.melagonaster, suggesting that haspin family members are found in a variety of eukaryotes. Among known kinases, haspin matches most closely with the cyclin-dependent and PAK/STE20 protein kinases. However, a number of features distinguish the haspin proteins from these and other kinase families (see Section 3), indicating that the haspin proteins should be classified as a new family of protein kinases (see classification of Hanks and Quinn, 1991; Higgins, unpublished). The N-terminal region of haspin does not show significant matches to other proteins in the databases, but it is likely that the DNA binding capacity of the mammalian haspins lies in this portion (Tanaka et al., 1999).