Figure 5.

Interaction of Arg-274 with Gln-441 is indispensable for regulated STAT1 activity. A, sequence homology of the loop between β9 and β10 of STAT family proteins. Secondary structure elements surrounding the loop are illustrated above the alignment. The sequences were aligned with ClustalW. B–E, transcriptional activities of the indicated mutants were assessed by the Dual-Luciferase reporter system. The RLU of the mutants were normalized against the value of wild-type STAT1 activity (B and C), R274Q (D), or R274P (E). The experiments shown in the lanes were performed in triplicate. The error bars represent S.D. of each condition. Asterisks, significant differences of the mean values of the mutant RLU compared with the mean values of the STAT1 RLU. p values were determined with Student's test: n.s., not significant; **, p < 0.01.