Developmental regulation of Drosophila imaginal disc proteins: synthesis of a heat shock protein under non-heat-shock conditions.

A low-molecular-weight heat-shock protein is reported here to be synthesized in Drosophila imaginal discs under non-heat-shock conditions. This protein has been identified as hsp 23 by its mobility in SDS-gel electrophoresis, by its isoelectric point, and by its partial proteolytic digest pattern. This protein is shown to be synthesized in tissue from late-third-instar larvae using both in vitro and in vivo radiolabeling techniques. Tissues from late-third-instar larvae synthesize hsp 23 at a level much higher than tissues from mid-third-instar larvae. The increased synthesis of this protein at the end of third instar coincides with the rise in ecdysone titer that occurs at this time of development. The developmental regulation of this protein suggests that hsp 23 plays a role in normal development as well as in the heat-shock response.