Expresses a fusion protein specifically from the 179 amino acid isoform translation initiation codon in M1-containing RNAs.
Contains tra2, with a 7 nucleotide insertion within exon 4. This tra2 fragment is fused in frame to a portion of the Ecol\lacZ gene. The 7 nucleotide insertion disrupts the open reading frames encoded by type A, B, and E spliced RNAs so that an enzymatically active lacZ reporter should only be produced from type C spliced RNAs.