Characterization of a DNA-binding factor that recognizes the 22-base pair trans-spliced leader sequence in Ascaris lumbricoides

Abstract

In nematodes, a subset of pre-mRNAs acquires a common 22 nucleotide 5'-terminal exon via transsplicing (see [1] for review). The donor molecule in trans-splicing is an approx. 100 nt, non-polyadenylated RNA, the spliced leader (SL) RNA. Genes encoding nematode SL RNAs are multicopy and usually, but not always, tandemly reiterated in association with 5S rRNA genes [1]. We have previously characterized genes encoding the SL RNA of the parasitic nematode, Ascar is lumbricoides and shown that SL RNA synthesis was catalyzed by RNA polymerase II [2]. We also determined that the SL RNA was accurately and efficiently transcribed in cell-free extracts prepared from 32-64 cell Ascar is lumbricoides embryos [3]. Subsequent mutational analysis established that efficient initiation of transcription in vitro depended upon two cis-acting DNA elements, a compact region centered approx. 50 nucleotides upstream of the