CLONING, SEQUENCING, AND GROWTH PHASE-DEPENDENT TRANSCRIPTION OF THE COENZYME F-420-DEPENDENT N-5,N-10-METHYLENETETRAHYDROMETHANOPTERIN REDUCTASE-ENCODING GENES FROM METHANOBACTERIUM-THERMOAUTOTROPHICUM DELTA-H AND METHANOPYRUS-KANDLERI

The mer genes, which encode the coenzyme F-420-dependent N-5,N-10-meth ylenetetrahydromethanopterin reductases (CH2=H(4)MPT reductases), and their flanking regions have been cloned from Methanobacterium thermoau totrophicum Delta H and Methanopyrus kandleri and sequenced. The mer g enes have DNA sequences that are 57% identical and encode polypeptides with amino acid sequences that are 57% identical and 71% similar, wit h calculated molecular masses of 33.6 and 37.5 kDa, respectively, In M . thermoautotrophicum, mer transcription has been shown to initiate 10 bp upstream from the ATG translation initiating codon and to generate a monocistronic transcript similar to 1 kb in length, This transcript was synthesized at all stages of M. thermoautotrophicum Delta H growt h in batch cultures but was found to increase in abundance from the ea rliest stages of exponential growth, reaching a maximum level at the m id-exponential growth phase. For comparison, transcription of the fir gene from M. thermoautotrophicum Delta H that encodes the formylmethan ofuran:tetrahydromethanopterin formyltransferase (A, A, DiMarco, K. A, Sment, J. Konisky, and R, S, Wolfe, J, Biol. Chem, 265:472-476, 1990) was included in this study, The ftr transcript was found similarly to be monocistronic and to be similar to 1 kb in length, but, in contras t to the mer transcript, the ftr transcript was present at maximum lev els at both the early and the mid-exponential growth stages.