Fig 4.

Precise mapping of the multiple transcription start sites in the MTF-1 gene. RNA was isolated from cells and subjected to S1 nuclease mapping with a labeled DNA oligonucleotide corresponding to the entire promoter region of MTF-1. While our β-globin reporter gene under these assay conditions yields a strong, narrowly defined site of transcription initiation (Westin et al 1987, and not shown), the MTF-1 promoter shows the scattered multiple starts characteristic of TATA-less, CpG-island type promoters. At least the longer transcripts are expected to allow for translation initiation from the AUG of uORF1 (framed) (see also Fig 3). Pr., position of input oligonucleotide probe (for details see Materials and Methods); C/T/A/G, sequencing reaction of the MTF-1 promoter region used as reference; “mMTF-1 transcripts” indicates the pattern of protection from S1 nuclease digest after hybridization of cellular mRNA to the probe oligonucleotide