El. Christian et M. Yarus, METAL COORDINATION SITES THAT CONTRIBUTE TO STRUCTURE AND CATALYSIS IN THE GROUP-I INTRON FROM TETRAHYMENA, Biochemistry, 32(17), 1993, pp. 4475-4480
We have used nucleoside phosphorothioates (NTPalphaS) and a substituti
on-interference method to identify phosphate oxygens that appear to be
important to guanosine cofactor addition in the self-splicing group I
intron from Tetrahymena thermophila. For the majority of these phosph
ate oxygens, however, the effect of NTPalphaS substitution is signific
antly reduced in reactions containing the added presence of manganese
ion (Mn2+) relative to magnesium ion (Mg2+) alone. The observed ''resc
ue'' of the NTPalphaS effect at these positions is thought to be due t
o the larger affinity of Mn2+ for sulfur. These data suggest the direc
t coordination of divalent metal ions within the highly conserved cata
lytic core of the Tetrahymena intron. Because many of these metal bind
ing sites appear to be in positions of close backbone-backbone approac
h, and adjacent to the guanosine binding site the splice junction, we
suggest roles for the corresponding ions in stabilizing tertiary struc
ture and substrate recognition and as participants in catalysis.