Abstract
We have determined the complete nucleotide sequence of beta h2, a pseudogene in the mouse beta-globin gene complex. The structure of beta h2 is analogous to that of a normal beta-globin gene, and its nucleotide sequence shares 72% homology with the coding regions of a reference mouse adult beta-globin gene. A frame shift occurs in the first coding region for which a compensatory splicing scheme can be devised. The reading frame is not otherwise disrupted. All of the recognized transcription, translation, and splicing signals in beta h2 are intact, with the exception of the " CCAAT box," which has been altered to GTAAC . We compared the predicted amino acid sequence of beta h2 with other beta-globin sequences. Evidence for a period of divergence without selection in the history of beta h2 was found in a set of codons that are usually highly conserved in productive beta-globin genes. An evolutionary tree constructed from nucleotide sequence suggests that beta h2 originated from the adult genes at least 60 million years ago. After some period as a productive gene, beta h2 was inactivated and has subsequently diverged without selection. Hybridization experiments demonstrated that beta h2 and the surrounding region occur without major alteration in other rodent species. The sequence ( AGCCA - 4n - GTGT ) occurs 5' of the CCAAT box in beta h2 and in many productive globin genes.
Highlights
From the Department of Microbiology and Immunology, Curriculumin Genetics, Program in Molecular Biology and Biotechnology, The Universityof North Carolinu, Chapel Hill, North Carolina 27514
An evolutionarytreeconstructed from nucleotide sequence suggests that Bh2 originated from the adult genesat least 60 million years ago.After some period as a productive gene, Bh2 was inactivatedand has subsequently diverged without selection
We show that Ph2 is a pseudogene: a n evolutionary remnant of a once active /3-globin gene
Summary
Sequencing Strategy"ph was sequenced by the chemical phates were purchased from P-L Biochemicals. If splicing occurs after position CCAAPy located 30-40 bases further upstreamis thought to 140 as in pZdminOr, the frame shift would be propagated be involved inpromotingtranscription [34] and is often into coding block 2 and lead to early termination of transla- referred to as the CCAAT box 298) adjacent to a region of 81% homology (base 299 to the We find that adult globin genes have a good match to splice site). Human [39] and goat [40]adult a-globin nodule leghemoglobin [33] This part of coding block 2 dem- genes similarlyhave a sequence like AGCCA-4n-GTGT overonstrates the characteristic divergence pattern of ph.
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