Origin of transcription of a mouse immunoglobulin light chain gene

Although the organization, the structure, and the somatic rearrangement of immunoglobulin genes have been studied in detail, there is no information regarding the precise origin of transcription of immunoglobulin genes. We have analyzed the 5'-flanking region of an expressed mouse V kappa light chain gene and the pre-mRNA transcript of that light chain gene, as it is expressed in vivo. Study of the pre-mRNA and of the DNA sequence by the procedure of "S1 mapping" establishes that the 5' end of the pre-mRNA transcript is 25-26 nucleotides upstream from the initiation codon. A CATATA sequence is found 22-23 nucleotides upstream from the origin of transcription. Although several other TATA-like sequences are found further upstream, only a single origin of transcription can be documented. From the S1 protection experiments, the 5' end of the mature mRNA was found to be the same as that of the pre-mRNA, indicating conservation of that sequence during RNA processing. Finally, a conspicuous pentanucleotide repeat CATTG - CATTG has been identified at the position of transcription initiation.