Bombyx Y-box protein BYB facilitates specific DNA interaction of various DNA binding proteins independently of the cold shock domain.

A new member of the Y-box protein family of the silkworm Bombyx mori (BYB) was co-purified with the fibroin gene enhancer-binding protein FMBP-1, and stimulated the binding of FMBP-1 to its cognate DNA element. However, the stimulatory effect was not specific to FMBP-1, BYB also enhancing the binding of mammalian transcription factors OTF2, SP1 and AP2 to their specific binding elements. Besides the above transcription regulatory factors, BYB facilitated the binding of basal transcription factor TBP, and enhanced transcription from the adenovirus 2 major late promoter in a reconstituted transcription system. Moreover, BYB stimulated the reactions of some restriction endonucleases under cold conditions. The C-terminal region of BYB was sufficient for these stimulatory effects, and the highly conserved cold shock domain (CSD) in the N-terminal region was dispensable. GST-pull down experiments showed that the C-terminal region could interact with DNA independently of the CSD. The above results suggest that the C-terminal region of BYB causes the active interaction of various DNA binding proteins with their targets. Such a function of the C-terminal region of BYB may partly explain the functional diversity of Y-box proteins.