Perspectives on tubulin isotype function and evolution based on the observation that Tetrahymena thermophila microtubules contain a single alpha- and beta-tubulin.
We have cloned and sequenced the two beta-tubulin genes of the ciliated protozoan Tetrahymena thermophila. The two genes encode identical 443 amino acid peptides which are 99.7% identical to the beta-tubulin proteins of T. pyriformis and 95% identical to human beta 1 tubulin. T. thermophila contains only one alpha-tubulin gene (Callahan et al., 1984: Cell 36:441-445). Thus, all of the extremely diverse microtubule structures in this unicellular organism can be formed from a single alpha- and a single beta-tubulin peptide. We have also carried out a phylogenetic analysis of 84 complete beta-tubulin peptide sequences. This analysis supports two hypotheses regarding beta-tubulin evolution and function: 1) Multifunctional beta-tubulins are under greater evolutionary constraint than beta-tubulins present in specialized cells or in cells with very few microtubule related functions, which can evolve rapidly; and 2) Cells which form axonemes maintain a homogeneous population of tubulins.
Gaertig
J
J
Department of Biology, University of Rochester, NY 14627.
Thatcher
T H
TH
McGrath
K E
KE
Callahan
R C
RC
Gorovsky
M A
MA
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000235:genetics; D008870:Microtubules / Q000737:chemistry* / Q000502:physiology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D013769:Tetrahymena pyriformis; D016808:Tetrahymena thermophila / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic; D014404:Tubulin / Q000032:analysis* / Q000235:genetics / Q000502:physiology*
D014404:Tubulin; D004247:DNA