Construction of cDNA libraries from intestine,mantle and hepatopancreas of hard clam (Meretrix meretrix) and ESTs analysis

The cDNA libraries of intestine,mantle and hepatopancreas of hard clam(Meretrix meretrix)were constructed with SMART cDNA Library Construction Kit.The libraries have a high titer of 2.10×10 6 ,1.70×10 6 and 1.60×10 6 ,respectively.The recombined efficiency of each cDNA library exceeded 95%.The all insert sizes of intestine library were over 1 kb,and the insert sizes over 1 kb in the mantle and hepatopancreas libraries were over 87.5%.Atotal of 3 168 clones of the libraries were randomly picked and sequenced from the 5'end of the cDNAs using a M13 universal primer,and 3 029 raw sequences of the ESTs were processed and then assembled into 1 796 unigene involving 306 contigs and 1 490 singletons.Blastx analysis showed that 696 unigenes(216 for intestine,235 for mantle and 245 for hepatopancreas)(38.75%)had significant homology(EvalueG10 -5 )to genes with known or putative functions in GenBank.The sequences containing microsatellite DNA(SSR)accounted for 3.1%of all ESTs indicating that SSR sequences were rich in the ESTs of hard clam.