Tissue and developmental expression of SRAM, an unconventional Rel-family protein

Previously we have reported the purification and cDNA cloning of a novel Rel/Ankyrin-family protein named SRAM from the flesh fly, Sarcophaga peregrina. Rel proteins generally translocate into the nucleus upon immune stimuli by dissociating from an inhibitory ankyrin domain, while SRAM is unique in terms of its constitutive nuclear localization with its internal ankyrin domain accompanied, at least in a Sarcophaga cell line and fat body cells. Although SRAM had been originally identified as a sole factor that binds to the κB motif of the inducible Sarcophaga lectin gene promoter, its transcriptional activity remained controversial. Moreover, homologues of SRAM have not been found in any other established model organisms including Drosophila. Here we report that the developmental expression of SRAM was up-regulated at the early stages of embryogenesis and metamorphosis. Furthermore, SRAM expression was prominent in the digestive tracts of the third instar larvae. We argue the hypothesis that SRAM has evolved as a quite unconventional Rel-family protein in Sarcophaga.