title: Identification of two human beta-tubulin isotypes.
abstract: The sequence of a human beta-tubulin cDNA clone (D beta-1) is described; our data revealed 95.6% homology compared with the sequence of a human beta-tubulin processed pseudogene derived by reverse transcription of a processed mRNA (Wilde et al., Nature [London] 297:83-84, 1982). However, the amino acid sequence encoded by this cDNA showed less homology with pig and chicken beta-tubulin sequences than the latter did to each other, with major divergence within the 15 carboxy-terminal amino acids. On the other hand, an independently isolated, functionally expressed genomic human beta-tubulin sequence (5 beta) possessed a very high degree of homology with chicken and pig beta-tubulins in this region. Thus, human cells appear to contain two distinct beta-tubulin isotypes. Both the intact beta-tubulin cDNA clone and a subclone containing only the 3' untranslated region detected two mRNA species in HeLa cells; these mRNAs were 1.8 and 2.6 kilobases long and were present in about equal amounts. Two independently subcloned probes constructed from the 3' untranslated region of the 5 beta genomic sequence also detected a 2.6-kilobase beta-tubulin mRNA. However, the 3'-untranslated-region probes from the cDNA clone and the genomic sequence did not cross-hybridize. Thus, at least two human beta-tubulin genes, each specifying a distinct isotype, are expressed in HeLa cells, and the 2.6-kilobase mRNA band is a composite of at least two comigrating beta-tubulin mRNAs.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002645:Chickens / Q000235:genetics; D003001:Cloning, Molecular; D004274:DNA, Recombinant; D005796:Genes; D006367:HeLa Cells; D006801:Humans; D009693:Nucleic Acid Hybridization; D010802:Phylogeny; D012333:RNA, Messenger / Q000235:genetics; D013552:Swine / Q000235:genetics; D014404:Tubulin / Q000235:genetics*
chemical_list: D004274:DNA, Recombinant; D012333:RNA, Messenger; D014404:Tubulin