Methyl coenzyme M reductase(MCR),catalyzing the final reaction in methanogens,is the key enzyme in the methane production pathway in methanogens.MCR gene clusters exist as mcrBDCGA in the genomes,5.8 kb.The sequence of the alpha subunit is very conservative,and the conservative sequence can be easily obtained.In this study,to obtain this gene cluster quickly and efficiently,four AD primers were designed according to the MCRB protein motifs and codon table.By TAIL-PCR,three of the four AD primers worked well and the correct fragments larger than 3 kb were obtained.The gene cluster cloned in this research would establish foundation for further studies of the enzyme.Compared with the traditional TAIL-PCR method,the improved TAIL-PCR in this research could obtain large target DNA fragments more easily.This experiment set an example for obtaining similar gene clusters.