AN ERYTHROID-SPECIFIC TRANSCRIPT GENERATES THE SOLUBLE FORM OF NADH-CYTOCHROME B(5) REDUCTASE IN HUMANS

Two forms of NADH-cytochrome bs reductase (b5R), an erythrocyte-restri cted soluble form, active in methemoglobin reduction, and a ubiquitous membrane-associated form involved in lipid metabolism, are produced f rom one gene. In the rat, the two forms are generated from alternative transcripts differing in the first exon, however, biogenesis of human b5R was less understood. Recently, two different transcripts (Ni and S), differing in the first exon were also described in humans. Here, w e have investigated the tissue-specificity and the role of the S-trans cript in the generation of soluble b5R. By RNase protection assays des igned to simultaneously detect alternative b5R transcripts in the same sample, the S transcript was undetectable in nonerythroid and in eryt hroleukemic K562 cells induced to differentiate, but was present in te rminal erythroblast cultures, and represented a major b5R transcript i n reticulocytes. Analysis of the translation products of the M- and S- transcripts in HeLa cells transfected with the corresponding cDNAs dem onstrated that the S transcript generates soluble b5R, presumably from an internal initiation codon. Our results indicate that the S-transcr ipt is expressed at late stages of erythroid maturation to generate so luble b5R. (C) 1998 by The American Society of Hematology.