A gene encoding the major beta tubulin of the mitotic spindle in Physarum polycephalum plasmodia
The multinucleate plasmodium of Physarum polycephalum is unusual among eucaryotic cells in that it uses tubulins only in mitotic-spindle microtubules; cytoskeletal, flagellar, and centriolar microtubules are absent in this cell type. The authors identified a ..beta..-tubulin cDNA clone, ..beta..105, which is shown to correspond to the transcript of the betC ..beta..-tubulin locus and to encode ..beta..2 tubulin, the ..beta.. tubulin expressed specifically in the plasmodium and used exclusively in the mitotic spindle. Physarum amoebae utilize tubulins in the cytoskeleton, centrioles, and flagella, in addition to the mitotic spindle. Sequence analysis shows that ..beta..2 tubulin is only 83% identical to the two ..beta.. tubulins expressed in amoebae. This compares with 70 to 83% identity between Physarum ..beta..2 tubulin and the ..beta.. tubulins of yeasts, fungi, alga, trypanosome, fruit fly, chicken, and mouse. On the other hand, Physarum ..beta..2 tubulin is no more similar to, for example, Aspergillus ..beta.. tubulins than it is to those of Drosophila melanogaster or mammals. Several eucaryotes express at least one widely diverged ..beta.. tubulin as well as one or more ..beta.. tubulins that conform more closely to a consensus ..beta..-tubulin sequence. The authors suggest that ..beta..-tubulins diverge more when their expression pattern is restricted, especially when this restriction results in their use in fewer functions. This divergence among ..beta.. tubulins could have resulted through neutral drift. For example, exclusive use of Physarum ..beta..2 tubulin in the spindle may have allowed more amino acid substitutions than would be functionally tolerable in the ..beta.. tubulins that are utilized in multiple microtubular organelles. Alternatively, restricted use of ..beta.. tubulins may allow positive selection to operate more freely to refine ..beta..-tubulin function.
- Research Organization:
- McArdle Lab. for Cancer Research, Univ. of Wisconsin, Madison, WI (US)
- OSTI ID:
- 5113254
- Journal Information:
- Mol. Cell. Biol.; (United States), Vol. 8:3
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
MICROTUBULES
STRUCTURE-ACTIVITY RELATIONSHIPS
PHYSARUM
CELL DIVISION
PROTEINS
AMINO ACID SEQUENCE
DNA BASE TRANSITIONS
GENETIC VARIABILITY
ALGAE
DNA-CLONING
DROSOPHILA
PHENOTYPE
TRYPANOSOMES
YEASTS
ANIMALS
ARTHROPODS
BIOLOGICAL VARIABILITY
CELL CONSTITUENTS
CLONING
DIPTERA
FLIES
FRUIT FLIES
FUNGI
INSECTS
INVERTEBRATES
MICROORGANISMS
MOLECULAR STRUCTURE
ORGANIC COMPOUNDS
PLANTS
550400* - Genetics
550700 - Microbiology
550200 - Biochemistry