Intracisternal A Particle Promoted Polypeptide (IPP)

Sequence of the 5-prime region of a genomic clone revealed the presence of a solo IAP LTR with the same U5 duplication, and primer extension analysis confirmed that transcription of the MIPP gene is under the control of the IAP LTR. Expression of the MIPP gene paralleled that of IAP genes in normal mouse tissues with abundant transcripts present in the placenta.

The MIPP-encoded protein is composed of four 48-amino acid units and shares homology with a vaccinia virus gene product. MIPP-related sequences were also found in several mammals, including the human genome. If the same placental-specific pattern of expression is seen in humans, an examination of the human IPP promoter could lead to important insights into the role of retroviruses in evolution.