title: In vivo discrimination among beta-tubulin isotypes: selective degradation of a type IV beta-tubulin isotype following overexpression in cultured animal cells.
abstract: Preceding efforts have revealed that tubulin synthesis in animal cells is regulated both by selective expression of individual members of the tubulin multigene families and by a post-transcriptional control pathway that cotranslationally degrades tubulin mRNAs when the concentrations of unassembled subunits are increased. To test the effect of forced expression of a specific beta-tubulin, we constructed Chinese hamster ovary (CHO) cell lines that stably express the chicken class IV (c-IV) beta-tubulin gene. After gene amplification, we obtained lines that synthesize the c-IV polypeptide at a rate two to three times that of all endogenous beta-tubulins. Despite this elevated rate of synthesis, these c-IV polypeptides accumulated to only 4 to 10% of cellular beta-tubulin. Furthermore, when c-IV transcription was further elevated transiently, there was a compensatory loss in the endogenous class IV isotype (m-IV) so that the total level of class IV isotypes remained unchanged. The data indicate that beta-tubulin isotypes I and IV are biochemically distinguished in these cultured cell lines and that the stability of individual isotypes is established in part by isotype-specific interactions with other cellular factors.
authors.affiliation: Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
authors.forename: S S
authors.initials: SS
authors.lastname: Sisodia
authors.forename: D A
authors.initials: DA
authors.lastname: Gay
authors.forename: D W
authors.initials: DW
authors.lastname: Cleveland
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D002645:Chickens / Q000235:genetics; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D005786:Gene Expression Regulation; D008870:Microtubules / Q000378:metabolism / Q000648:ultrastructure; D008969:Molecular Sequence Data; D010053:Ovary; D011499:Protein Processing, Post-Translational; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D014404:Tubulin / Q000145:classification / Q000235:genetics / Q000378:metabolism*
chemical_list: D011993:Recombinant Fusion Proteins; D014404:Tubulin