SpP3A2

Function

SpP3A2 codes for transcription factor.
It is a negative spatial regulator of CyIIIa expression.
SpP3A2 factor represses the expression of CyIIIa gene in oral ectoderm by binding to two P3A sites in the proximal module (Zeller et al., 1995).

Protein

The SpP3A2 protein has no significant similarity to any previosly reported protein sequence.
The sequences essential for the DNA-binding activity of SpP3A2 span a broad region, the N-terminus of which occurs between amino acid positions 25-90, and the C-terminal boundary between residues 222-358, i.e. a DNA-binding domain of SpP3A2 includes at least 130 amino acids.
SpP3A2 DNA binding domain shows no similarity to any previously characterized DNA-binding motif. SpP3A2 is thus a novel, sequence specific recognition factor.
Two regions of SpP3A2 are relatively rich in serine and theonine and may include sites of phosphorilation detected in the affinity-purified protein (Calsone et al., unpublished observations).
Near the N terminus, the sequence spanning residues 4 to 28 is 36% serine plus theonine (S+T); residues 266-290 are 28% (S+T) and residues 364-389 are 26,9% (S+T). The remaining sequences in SpP3A2 are average 11,7% (S+T).
This protein also has a very glutamine-rich region, similar to those detected in Oct-1 and Zeste. Thus, the SpP3A2 sequence between residues 308 and 336 is 37,9% glutamine, compared to 6,7% glutamine in the premainder of the protein (Hoog et al., 1991).
Most likely, SpP3A2 factor binds DNA as a dimer (Zeller et al., 1995).

Subcellular location

Egg cytoplasm and pronuclus, embryonic nuclei (Zeller et al., 1995).

Expression Pattern

Maternal SpP3A2 mRNA is present in unfertilized egg.
It is very low-abundance factor. There are about 1100 copies of the SpP3A2 mRNA per egg (Hoog et al., 1991). At its peak in mid-late cleavage the average blastomere nucleus contains about 3000 molecules of SpP3A2, but there are only about 1200 molecules/nucleus at blastula stage. This level remains approximately constant at least through the late gastrula period. (Calzone et al., 1991).

The average SpP3A2 protein level (molecules/nucleus)
Method: Immunological blot reaction
Reference: Zeller et al., 1995

Stage Egg pronucleus 5 hr 10 hr 24 hr 36 hr 48 hr

Level 1.71*10^4 5*10^3 9*10^3 1.4*10^4 1*10^4 7*10^3