In Volvox carteri, regA acts as a master gene to suppress all germ cell functions in somatic cells. Its product, RegA, has features of a transcriptional repressor. Here we report cDNA sequences ...representing 15 nuclear genes with properties expected of RegA targets: they are expressed strongly in germ cells and in regA-, but not regA+, somatic cells. Two of them encode polypeptides with no recognizable features, but ten (like three previously sequenced ones) encode chloroplast proteins of known function, and the remaining three encode putative chloroplast proteins of unknown function. This suggests that RegA blocks reproductive development in somatic cells by preventing chloroplast biogenesis, thereby making it impossible for the cells to grow enough to reproduce.
Microtubules (MT) carry out several specialized morphogenetic functions in the multicellular green alga Volvox
carteri (Vc), in addition to functions also executed in its closest unicellular ...relative,
Chlamydomonas reinhardtii (Cr). To find out if these differences in morphogenetic complexity are reflected in tubulin (Tub) differences, we have compared the Vc
αtub and
βtub genes with their
Cr counterparts. The Vc genome contains two
αtub and two
βtub genes. We report here the sequences of the
α2tub and
β2tub genes, and thus complete the set of four
tub sequences. The two
αtub and two
βtub genes code for identical 451 (α) and 443 (β) amino acid (aa) polypeptides; they differ from the
Cr homologs in two (α) and one (β) residues, respectively. Silent nucleotide (nt) exchanges between sibling genes are much more frequent in Vc than in
Cr (12 vs. 2%), probably owing to a more stringent codon bias in the latter alga. Transcription of
α2tub and
β2tub starts with an A, 26 by (α
2) or 25 by (β
2) downstream from the TATA box. A 16-bp promoter element upstream and a G+C-rich sequence downstream from the TATA box are conserved in all
tub of both species. Moreover, a 28-bp element of conserved sequence, and hence of possible functional significance, was found at similar locations in the 5′ untranslated region (UTR) of all four
αtub. A conserved TGTAA downstream from the translation stop codon represents the algal poly(A)-addition signal (in both Vc and
Cr). Northern analyses and reverse transcription (RT) followed by polymerase chain reaction have demonstrated that all four
tub RNAs are present at all stages of the Vc life cycle
The 11 alpha-hydroxylase of progesterone was induced in the filamentous fungus Rhizopus nigricans ATCC 6227b with different steroids as inducers and the induction process was optimized in regard to ...the age of the mycelium, to the concentration of the inducer and to the time of induction. Deoxycorticosterone and testosterone, steroids with higher polarity of the side-chain than progesterone, although poorer substrates for in vivo hydroxylation than progesterone, induced more enzyme compared to progesterone. Other alterations in the steroidal ring system examined diminished the induction capability of the inducing steroid to different extent. The highest 11 alpha-hydroxylating activity, if expressed on the basis of mycelial wet weight, was achieved with 18 h old mycelium which was induced for 2 h with 0.30 mM deoxycorticosterone.
