Fig. 5. XNIF-LE is recognized by specific proteins from Xenopus oocyte extract. RNA binding was assayed in vitro by UV cross-linking. RNA-binding reactions contained ³²P-labeled lacZ-tag RNA (lanes 1 and 2), lacZ-tag-XNIF-LE (252-551) (lanes 3-8), lacZ-tag-XNIF nt 252-381 (lanes 9, 10 and 11), lacZ-tag-XNIF nt 252-381 in a tandem repeat (nt 252-381-tr, lanes 12, 13 and 14) or lacZ-tag-Vg1-LE (lanes 15, 16 and 17) transcripts, S100 extract, and either solely tRNA competitor (1, 3, 9, 12 and 15), additional non-specific lacZ-tag competitor RNA (lanes 2, 4, 10, 13 and 16) or sequence specific competitor RNA, as indicated (lanes 5, 11, 14 and 17). For the XNIF-LE (252-551), additional unlabeled competitor and cross-competitor RNAs have been analyzed: Vg1LE (lane 6), XNIF nt 252-381 (lane 7) and XNIF nt 252-381 in a tandem repeat (lane 8). Cross-linked proteins were analyzed and detected by 10% SDS-PAGE and phospho-imaging. Specifically interacting proteins are marked by asterisks. Proteins that exclusively bound to the LE of the early pathway RNA XNIF are marked by red asterisks.