Characterization of two cDNAs encoding serine proteinases from the hard tick Haemaphysalis longicornis

Host vaccination against tick infestation is at present the most practical and sustainable alternative tick control method to the current acaricide us e which has serious limitations. However the success of this approach to co ntrol ticks depends upon the identification of target vaccine antigens. Mem bers of the serine proteinase gene family may represent an interesting grou p of proteins to target as candidate antigens because of their involvement in regulation of many physiological functions and development processes in a wide range of organisms. We used RT-PCR with the 3' and 5' RACE to clone two cDNAs encoding full-length serine proteinases from the hard tick, Haema physalis longicornis. RT-PCR degenerate primers were designed from amino ac id sequences surrounding active sites, His(57) and Ser(195) conserved among most known serine proteinase. Gene specific primers designed from nucleoti de sequences of the RT-PCR products were used to prime the 3' and 5' RACE. Southern blotting analysis showed that both HLSG-1 and -2 are single copy. The 2 cDNAs, HLSG-1 and -2 are 1.2 and 1.0 kb long in size with open readin g frames encoding polypeptides with 37.7 and 31.2 kDa predicted molecular m ass respectively. Northern blotting analysis of total RNA from unfed and pa rtially fed whole ticks showed that the expression of mRNAs for both HLSG-1 and -2 was induced by blood feeding. Expression analysis by RT-PCR showed that both HLSG-1 and -2 are expressed in other tick organs in addition to s alivary glands and midguts. The 6 serine proteinase consensus cyteine resid ues are well conseverd in both HLSG-1 and -2. We have discussed our finding s with respect to tick vaccine development research. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.