A retropseudogene for non-histone chromosomal protein HMG-1.

Southern analysis of the human genome revealed that there are several sequences with homology to the nonhistone chromosomal protein HMG-1. The majority of the HMG-1 sequences are intronless as suggested from the polymerase chain reaction of HeLa DNA. Sequencing of a clone from a human placenta genomic library revealed that the clone was intronless and displayed 99% homology to the human HMG-1 cDNA. The 5' regulatory motif, CCAAT, is present in the clone but there is no TATA-box. Most of the differences between the HMG-1 cDNA sequence and the clone involve point mutations with no interruption of the reading frame. The sequence is flanked at 5' and 3' ends by a 15 nucleotide long direct repeat suggesting that the clone is a processed HMG-1 retropseudogene. Sequence differences between the reading frames of the HMG-1 pseudogene and HMG-1 cDNA indicated that the pseudogene arose relatively late in evolution, approximately one million years ago. The present paper is the first study on a genomic sequence related to HMG-1 genes.