MOLECULAR CHARACTERIZATION OF RAT CRRY - WIDESPREAD DISTRIBUTION OF 2ALTERNATIVE FORMS OF CRRY MESSENGER-RNA

The rat complement regulator 512 antigen/Crry is present in a widespre ad distribution as at least two discrete proteins of M(r) 65 000 - 70 000 and 75 000 - 85 000. The molecular basis for the different protein s has not been determined. We screened a cDNA library derived from cul tured rat glomerular epithelial cells with a polymerase chain reaction (PCR)-generated nucleotide probe for CR1 and Crry. Two identical clon es with 1.8 kilobase inserts were obtained. Clone 6.1 consisted of 181 1 nucleotides. The sequence was identical to nucleotides 42 - 1666 of the cDNA for rat 512 antigen/Crry except for 11 nucleotides at the ext reme 5' and 3' ends and an exact duplication of 186 bases that would e ncode an additional complete short consensus repeat (SCR). By reverse transcription PCR, we show that the two forms of Crry mRNA exist in al l rat cells/ tissues examined. It is likely that these two Crry mRNA s pecies differ by the absence or presence of a 186 base repeat that enc odes a complete SCR. These are translated into Crry proteins, containi ng six and seven SCRs, respectively, which explains the different size s of Crry proteins. The role of the SCR duplication remains to be defi ned.