Host cell protein sequence search - (Mar/01/2013 )

I want to look for a specific motif in well-known host-cell proteins that are involved in transcription, translation, even signalling. Ideally I would like to search all of these proteins for a specific ~5 amino acid sequence at once. Where can I get the sequence of such proteins? Is there a specific site that would have most well-known host cell protein sequences?

Please share any websites, tips, etc.

Thanks,

JM

try Expasy/UniprotKB/Swissprot (web.expasy.org)