Alternatively spliced transcripts of the human complement C2 gene.

To investigate the possible presence of alternatively spliced C2 gene transcripts, we amplified mRNA from HepG2 cells by reverse transcription-PCR using primers derived from the 5' and 3' untranslated regions of the C2 mRNA. Cloning of the resulting products revealed the presence of four novel C2 mRNA size variants. Nucleotide sequencing indicated that the variant mRNAs were probably derived through differential splicing of C2 gene transcripts. Specifically, nucleotide sequence deletions in the four variant mRNAs could be attributed to splicing out of: 1) exons 2 and 3; 2) exon 3; 3) exon 17; and 4) exons 6 and 7 and the 5' region of exon 18. The results were confirmed by RNase protection assays using HepG2 mRNA. Inspection of the nucleotide and the deduced amino acid sequences indicated that in the first two variants the alternative splicing did not affect the C2 open reading frame. In the other two variants, frameshifts in exon 18 resulted in termination codons up- or downstream of the authentic termination codon. All four variants C2 mRNAs were capable of encoding truncated C2 proteins, and were detected by reverse transcription-PCR not only in HepG2 cells but also in human liver, U937, and U105-MG cells. The latter analyses indicated the presence of an additional C2 mRNA variant lacking the region encoded by exon 6.