2 DIFFERENT PROMOTERS DIRECT EXPRESSION OF 2 DISTINCT FORMS OF MESSENGER-RNAS OF HUMAN PLATELET-ACTIVATING-FACTOR RECEPTOR

The human platelet-activating factor (PAF) receptor gene exists as a s ingle copy on chromosome 1. We identified two 5'-noncoding exons, each of which has distinct transcriptional initiation sites. These exons a re alternatively spliced to a common splice acceptor site on a third e xon that contains the total open reading frame to yield two different species of functional mRNA (Transcript 1 and 2). Transcript 1 has cons ensus sequences for transcription factor NF-kappaB and Sp-1, and the I nitiator (Inr) sequence homologous to the murine terminal deoxynucleot idyltransferase gene. Transcript 2 also contains consensus sequences f or transcription factor AP-1, AP-2, and Sp-1. Transcripts 1 and 2 were both detected in heart, lung, spleen, and kidney, whereas only Transc ript 1 was found in peripheral leukocytes, a differentiated human eosi nophilic cell line (EoL-1 cells), and brain. Existence of distinct pro moters was thus suggested to play a role in the regulatory control of PAF receptor gene expression in different human tissues and cells.