Structural variation among human beta-tubulin genes.

The interphase cell of Crithidia fasciciulata has three discrete tubulin populations: the subpellicular microtubules, the axonemal microtubules, and the nonpolymerized cytoplasmic pool protein. These three tubulin populations were independently and selectively purified, yielding, in each case, microtubule protein capable of self-assembly. All three preparations polymerized to form ribbons and sheets rather than the more usual microtubular structures. Analyses of the tubulin by two-dimensional polyacrylamide gel electrophoresis, isoelectric focusing, and peptide mapping indicated that the beta-tubulin complex remained constant regardless of source but that some heterogeneity was present in the alpha subunit. Cytoplasmic pool alpha tubulins (alpha 1/alpha 2) were the only alpha isotypes in the cytoplasm and also formed most of the alpha tubulin species in the pellicular fraction. Flagellar alpha tubulin (alpha 3) was the sole alpha isotype in the flagella; it appeared in small amounts in the pellicular fraction but was completely absent from the cytoplasm. In vitro translation products from polyadenylated RNA from C. fasciciulata were also examined by two-dimensional polyacrylamide gel electrophoresis and possessed a protein corresponding to alpha 1/alpha 2 tubulin but lacked any alpha 3 tubulin. The alpha 3 polypeptide arose from a posttranslational modification of a precursor polypeptide not identifiable by two-dimensional polyacrylamide gel electrophoresis as alpha 3. Peptide mapping data indicated that cytoplasmic alpha tubulin is the most likely precursor. These results demonstrate alpha-tubulin heterogeneity in this organism and also how close the relationship between flagellar and cytoskeletal tubulins can be among lower eucaryotes.Microtubules are present in most eucaryotic cells where they fulfill a diverse range of functions vital to the existence of the cell. Until recently, tubulin research has been conducted almost exclusively on protein isolated from mammalian brain tissue. Although invaluable to our current understanding of the physical properties of the protein, it has been of limited value to our appreciation of the roles of tubulin polypeptides within the cell. What is becoming increasingly obvious is that, despite its conserved nature, tubulin exists as a family of proteins. As the range of organisms from which tubulin has been purified broadens the extent of the diversification of the protein becomes clearer. In this context, eucaryotic microbes are particularly useful since, unlike most metazoan cells, they possess rigorously organized cytoskeletons, often with highly ordered microtubular organelles devoted to specific activities. It is, therefore, easier to examine the microtubular proteins and also to predict the constraints under which the microtubules in such organelles would operate.

mentioning

confidence: 99%

Tubulin heterogeneity in the trypanosome Crithidia fasciculata.

Russell¹,

Miller²,

Gull³

1984

“…Most organisms studied to date have large tubulin multigene families, ranging from 10 to 20 unique DNA fragments per genome (1,6,8,28). However, within mammals, many of these sequences are pseudogenes (8.…”

mentioning

confidence: 99%

Differential expression of two neural cell-specific beta-tubulin mRNAs during rat brain development.

Bond¹,

Robinson²,

Farmer³

1984

We recently demonstrated that j3-tubulin mRNA expression is regulated during rat brain development. This is manifested by a dramatic decrease in both 1.8-and 2.9-kilobase (kb) mRNAs when extensive neurite elongation is occurring. Coincident with these decreases is the increased production of a 2.5-kb mRNA. (J. F.Bond and S. R. Farmer, Mol. Cell. Biol. 3:1333-1342. In the present study, we have isolated and characterized three different cDNAs corresponding to I8-tubulin mRNAs (RIIT.1, RjiT.2, and R,BT.3).Hybridization of 3' untranslated region subclones of RO1T.1 and R,IT.2 cDNAs to RNA from a variety of rat tissues and cells revealed that these two cDNAs are neural cell specific. ROT. 1 corresponds to an abundant 1.8-kb mRNA expressed only at early stages of rat brain development. RO1T.2 corresponds to the 2.5-kb mRNA expressed at later stages. These data strongly suggest that there is differential expression of the Il-tubulin multigene family during rat brain development.

“…Since the apparent relative rates of RNA transcription were similar in both cell types, we conclude that the reduction in relative levels of the a-tubulin and p94 RNAs in the cell depends largely on the relative stability of the two RNAs and not on the relative rates of transcription. The faster disappearance of the two RNA species relative to other cellular RNAs from actinomycin D-treated PYS-2 compared with F9 cells is consistent with this interpretation.Microtubules consist of two proteins, a-and ,B-tubulin, each shown in human, chicken, and Drosophila melanogaster to contain several distinct genes (7,8,10,20,37,46). In D. melanogaster, members of the a-and P-tubulin multigene families are differentially expressed during embryonic development and in different adult tissues (21,23,31,35).…”

mentioning

confidence: 99%

“…Microtubules consist of two proteins, a-and ,B-tubulin, each shown in human, chicken, and Drosophila melanogaster to contain several distinct genes (7,8,10,20,37,46). In D. melanogaster, members of the a-and P-tubulin multigene families are differentially expressed during embryonic development and in different adult tissues (21,23,31,35).…”

mentioning

confidence: 99%

Post-transcriptional regulation of the abundance of mRNAs encoding alpha-tubulin and a 94,000-dalton protein in teratocarcinoma-derived stem cells versus differentiated cells.

Howe¹,

Lugg²,

Overton³

1984

Changes in the expression of the genes encoding a-tubulin and a 94,000-dalton protein (p94) specified by a cDNA clone, p4-30, were examined in a differentiated teratocarcinoma-derived parietal endoderm cell line, PYS-2, and an undifferentiated teratocarcinoma stem cell line, F9. Relative to other proteins or mRNA species, the synthesis rate of the a-tubulins and of p94, as well as the levels of their corresponding cytoplasmic mRNAs, were lower in PYS-2 than in F9 cells. The decrease was greater for the relative abundance of cytoplasmic a-tubulin mRNA than for p94 mRNA. Similarly, induction of differentiation of F9 cells by simultaneous exposure to retinoic acid (RA) and dibutyryl cyclic AMP resulted in reduced relative levels of the cytoplasmic mRNAs for these proteins. The reduction in abundance of the two RNA species was not due to a decrease in growth rate since the differentiated cells, PYS-2, RA-treated F9, and RA plus dibutyryl cyclic AMP-treated F9 cells, grew at a rate similar to that of undifferentiated F9 cells. However, induction of differentiation of F9 cells by treatment with RA alone did not cause down-regulation of the two RNA species. The relative levels of total cellular RNA encoding ca-tubulin and p94 in PYS-2 cells were also lower than those in F9 cells to an extent comparable to the decrease in the cytoplasmic RNAs. Since the apparent relative rates of RNA transcription were similar in both cell types, we conclude that the reduction in relative levels of the a-tubulin and p94 RNAs in the cell depends largely on the relative stability of the two RNAs and not on the relative rates of transcription. The faster disappearance of the two RNA species relative to other cellular RNAs from actinomycin D-treated PYS-2 compared with F9 cells is consistent with this interpretation.Microtubules consist of two proteins, a-and ,B-tubulin, each shown in human, chicken, and Drosophila melanogaster to contain several distinct genes (7,8,10,20,37,46). In D. melanogaster, members of the a-and P-tubulin multigene families are differentially expressed during embryonic development and in different adult tissues (21,23,31,35). However, little is known about the regulation of synthesis of these proteins during murine embryogenesis, though changes in protein synthesis have been demonstrated (17) to occur during early embryonic development. A recent study (9) showed that treatment of Chinese hamster ovary cells with the microtubule-depolymerizing drug colchicine resulted in the specific and rapid loss of tubulin mRNA from the cytoplasm. It was suggested that this loss of tubulin mRNA was probably not achieved through a transcriptionally regulated mechanism since the relative rates of tubulin RNA transcription are essentially unchanged in isolated nuclei derived from colchicine-treated and untreated control cells (6). In contrast, expression of globin genes in a hemintreated human erythroid cell line (5) and of a-fetoprotein and albumin genes in liver from late prenatal to 1-month-postpartum mice (43) is regulated primar...