of brlf1 3 u2032 utr seq id no 16 hereinafter referred to as brlf1m1 using an ezchange u2122 site directed mutagenesis kit enzynomics daejeon south korea moreover the region corresponding to 5 u2032 ccugcu 3 u2032 in target site 2 was mutated to 5 u2032 gcucga 3 u2032 to produce a mutant of brlf1 3 u2032 utr seq id no 17 hereinafter referred to as brlf1m2 using an ezchange u2122 site directed mutagenesis kit enzynomics daejeon south korea furthermore in the brlf1 3 u2032 utr the regions corresponding to 5 u2032 ccugcu 3 u2032 in target site 1 and target site 2 were all mutated to 5 u2032 gcucga 3 u2032 to produce a mutant of brlf1 3 u2032 utr seq id no 18 hereinafter referred to as brlf1m1m2 using an ezchange u2122 site directed mutagenesis kit enzynomics daejeon south korea the respective mutant genes were amplified using a pair of primers of seq id nos 19 and 20 a pair of primers of seq id nos 21 and 22 and psic brlf1 and psic bzlf1 plasmids as templates the constructed plasmids were named a psic brlf1m1 plasmid a psic brlf1m2 plasmid a psic brlf1m1m2 plasmid and a psic bzlf1m1 plasmid respectively the primers used for the amplification of the respective genes are shown in the following.