The TATA binding protein in the sea urchin embryo is maternally derived

The cDNA encoding the TATA binding protein was isolated from 8- to 16-cell and morula-stage embryonic libraries of two distantly related species of se a urchin, Strongylocentrotus purpuratus and Lytechinus variegatus, respecti vely. The two proteins are 96% identical over both the N- and C-terminal do mains, suggesting a conservation of transcriptional processes between the t wo species. The prevalence of SpTBP transcripts at several developmental ti me points was determined using the tracer excess titration method, and the corresponding number of TBP protein molecules was determined by quantitativ e Western blot analysis. Our results indicate that the amount of TBP mRNA a nd protein per embryo remains relatively constant throughout development. A n initial large pool of TBP protein (>10(9)) molecules in the egg becomes d iluted as a consequence of cell division and decreases to about 2 x 10(6) m olecules per cell by the gastrula stage. We found by in situ RNA hybridizat ion that the oocyte contains a large amount of TBP mRNA which is depleted l ate in oogenesis so that the eggs and early embryos have extremely low leve ls of TBP mRNA. We conclude that the oocyte manufactures nearly all of the TBP protein necessary for embryogenesis. (C) 1998 Academic Press.