TABLE 2.

 Yeast HisRS aminoacylation of microhelix^His variants

^aAll microhelices were synthesized with a 5′ monophosphate except the HO-G:A variant. Nonstandard bases are abbreviated as follows: Neb, nebularine; I, inosine; dAb, 2′-deoxyabasic; 2AP, 2-aminopurine; 7DAG, 7-deaza-2′-deoxyguanine; isodG, 2′-deoxyisoguanine; and isoC, isocytidine.

^bValues are the average of at least three determinations with SDs of ≤25%. The value for the C:I mutant is the result of two determinations. Values reported for substrates derived from the S. cerevisiae sequence are relative to the wild-type S. cerevisiae microhelix, which was set at 1.0. (The absolute value is reported in Table 1.) E. coli microhelix^His (G:C) is aminoacylated by yeast HisRS with a 3.3-fold reduced efficiency relative to yeast microhelix^His. Values reported for substrates derived from the E. coli sequence are relative to the wild-type E. coli microhelix, which was set at 1.0.

^c−ΔΔG^‡ is defined as RTln[(k _cat/K _M)^variant/(k _cat/K _M)^wild-type], where R = 1.98272 cal/mol  ;·  ;K and T = 303 K.

^dValues in parentheses are corrected for the deoxy effect.