FIG. 1.

(A) Delineation of the SU(S) RNA binding domain. MBP-SU(S) fusion proteins containing different portions of the first 360 amino acids of SU(S) were evaluated for binding to radioactively labeled ftz pre-mRNA by nitrocellulose filter binding or blot overlay assays. Plus symbols indicate binding; minus symbols indicate no binding. The horizontal solid line indicates the region included in each fusion protein. The shaded vertical bars indicate the two RNA binding regions defined from this analysis, and the amino acid sequence of each region is shown beneath the schematic figure. Arginine residues are indicated in bold type. (B) Amino acid sequence of the N-terminal 434 amino acids of SU(S). The amino acids deleted in the SU(S) ΔARM mutants are shown in bold type. The two zinc binding motifs are underlined, and the cysteine (C) and histidine (H) residues that are characteristic of this motif are shown in bold type.