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Abstract
Ribosomal protein methylase has been purified from Escherichia coli strain Q13 using
methyl-deficient 50S subunits as substrates. The purified enzyme (or enzyme complex)
which is devoid of rRNA methylating activity is quite stable and has a pH optimum
around 8.0. The Km for S-adenosyl-L-methionine is 3.2 muM. The molecular weight of
the enzyme is 3.1 X 10(4); minor methylating activity was also detected for protein
peaks with molecular weights of 1.7 X 10(4) and 5.6 X 10(4). Protein L11 is the major
protein methylated by the purified enzyme. Product analysis revealed the presence
of N epislon-trimethyllysine, a methylated neutral amino acid(s) previously observed
in protein L11 and N epislon-monomethyllysine. Free ribosomal proteins were much better
substrates for the methylation, indicating that methylation of 50S ribosomal proteins
can occur before the complete assembly of the 50S ribosomal subunit.