CAATTG-SPECIFIC RESTRICTION-MODIFICATION MUNI GENES FROM MYCOPLASMA -SEQUENCE SIMILARITIES BETWEEN R-CENTER-DOT-MUNI AND R-CENTER-DOT-ECORI

The genes coding for the MunI restriction-modification (R-M) system, w hich recognize the sequence 5'-CAATTG, have been cloned and expressed in Escherichia coli, and their nucleotide sequences have been determin ed. The restriction endonuclease (ENase; R MunI) is encoded by an open reading frame (ORF) of 606 bp, and a 699-bp ORF codes for the methylt ransferase (MTase). The two genes are transcribed divergently from a 3 55-bp region. The gene encoding the ENase is preceded by a short co-li near ORF of 222 bp. The deduced amino acid (aa) sequence of this short ORF (SORF) closely resembles the sequences of a family of regulatory proteins that are associated with other type-II R-M systems. Comparati ve analysis of the deduced aa sequence of R.MunI revealed several regi ons of similarity to the EcoRI and RsrI ENases that recognize the GAAT TC sequence. The similar mode of interaction of MunI, EcoRI and Rsr I with the tetranucleotide AATT, common to the recognition sequences of these ENases, was suggested.