Table 4.

Decoding properties for UAG and UGA of M. barkeri tRNA^Pyl and E. coli tRNA^Sec

tRNA	Anticodon	lacZ codon (mutation)	Suppression efficiency, %
tRNAPyl	CUA	UAG (A24)	100
tRNAPyl	CUA	UGA (U4)	<1
tRNAPyl	UCA	UAG (A24)	<1
tRNAPyl	UCA	UGA (U4)	81
tRNASec	CUA	UAG	68*
tRNASec	CUA	UGA	<1*
tRNASec	UCA	UAU	<1*
tRNASec	UCA	UGA	100*

Suppression efficiency was measured by β-galactosidase activity in E. coli strain XAC/U4 (for opal) and in E. coli strain XAC/A24 (for amber). In the absence of Cyc, background suppression in all cases was <5%.

*Suppression efficiencies for tRNA^Sec are from ref. 19.