In　order　to　verify　the　function　of　genD1,　a　recombinant　plasmid　pGD14　was　constructed　for　blockingup　genD1.　pGD14　was　introduced　into　Micromonospora　purpurea　GK1101　(ΔgenK))　by　conjugation.　A　desired　mutant　strain　GD1989　was　obtained　by　PCR　analysis.　Flask　shaking　experiments　and　MS　analysis　showed　that　the　mutant　strain　GD1989　only　produced　gentamicin　A　instead　of　gentamicin　C　complex,　and　the　product　of　GD1989　feeding　on　gentamicin　X2　contained　gentamicin　C　complex.　It　was　speculated　that　genD1　gene　might　be　responsible　for　methylation　at　C-4＂　of　garosamine.