[BioC] Ensembl mouse proteins

[Stefanie Carola Gerstberger]

Hi,
I have tried to download the mouse protein sequences from Biomart Ensembl.  I only received 2203 protein sequences for mouse, including isoforms. The same results from downloading the Ensembl protein sequences through UCSC genome browser.I also encounter the problem for Xenopus tropicalis - only 4700 protein sequences. As reference point S.cerevisae has  6700 sequences in Ensembl biomart, human 87,000, Drosophila 22,000. Does anyone know why this is and how I can circumvene this problem to get a complete list of protein sequences for mouse and Xenopus?
Thanks,
Stefanie