The 70 ku HSPs are responsible for intracellular chaperone and extracellular immunoregulation,which play crucial roles in protecting cells against environmental stresses,such as heat shock,heavy metals,drought,disease and parasitization.In this researchpartial cDNA sequence of HSP70 was cloned from Mytilus coruscus.BLAST analysis and phylogenetic relationship strongly suggested that this sequence was a member of HSP70 family and highly homologous with other known HSP70 of bivalve,especialy with Mytilus galloprovincialis(96%),and they gathered into the same branch in the evolutionary tree.In heat shock of 37 ℃,the expression of HSP70 in gill and hepatopancreas was up-regulated rapidly and was 30 times higher than that of control mussels after 2 h.Then the expression increased as time went on,and reached the maximum peak approximately 100-fold in hepatopancreas,which showed that HSP70 of M.coruscus was thermal induced protein.The mRNA of HSP70 in hepatopancreas and gills after infection by Escherichia coli and Bacillus subtilis,which were common microorganisms in water,was detected based on RT-PCR analysis.The temporal expression of HSP70 mRNA was upregulated,especially in the group of E.coli challenge.The maximum level in hepatopancreas and gills appeared at 8 h post-injection with 4.0-fold in gills and 4.5-fold in hepatopancreas,and then dropped back to the original level at 48 h post-injection.In Bacillus subtilis infection,the transcripts of HSP70 in hepatopancreas was induced to the highest at 6 h after post-injection with 2.5-fold,which was similar to the effect of PBS injection.In gills the mRNA of HSP70 increased slowly to the highest at 8 h with 4-fold,then decreased quickly,and returned gradually to physiological level at the end of this experiment.All these results indicated that HSP70 in M.coruscus played a significant role in regulating the environmental stress and immune response.