Abstract:

【Objective】 To better understand the origination and evolution of lef-3 gene from baculovirus genome and determine the relationships between various viruses at molecular level. 【Method】 Late expression factor 3 gene (lef-3) fragments of Pieris rapae granulovirus was obtained through conventional PCR method, sequenced after being cloned into T-vector. Then, bioinformatics analysis on lef-3 gene and its encoding sequences were conducted by using bio-softs. 【Result】 The DNA fragment was cloned and 4 mutations were appeared ,which did not alter the sequences of amino acids. It was inferred that PiraGV LEF-3 protein contained 399 amino acids ,the total molecular of which was 3.99 kD. Prediction of the lef-3 advanced structure and homology comparison between its encoding sequences and other LEF-3 genes from various baculoviruses showed that the lef-3 gene might encode the single strand DNA-binding protein .The result of blast revealed that the lef-3 gene only existed in Lepidoptera host for the baculovirus genome,and the evolution analysis illustrated that lef-3 gene could be divided into three groups including one GV genus and two NPV genus. The selection pressure analysis of GV's lef-3 gene coding region showed that the majority of lef-3 genes performed negative selection, while the Ka/Ks differed from different lef-3 genes, to some extent ,which also performed positive selection. The origination analysis revealed that lef-3 gene of baculovirus might derive from bacteria. 【Conclusion】 The lef-3 gene of PiraGV was cloned successfully and speculations upon the possible pattern of origination and evolution were made through bioinformatics analysis.

Key words: Pieris rapae granulovirus, late expression factor 3 (LEF-3), single-stranded DNA-binding protein (SSB), evolutionary origin