ON THE ORIGIN OF MESSENGER-RNA ENCODING THE TRUNCATED DOPAMINE D-3-TYPE RECEPTOR D-3NF AND DETECTION OF D-3NF-LIKE IMMUNOREACTIVITY IN HUMAN BRAIN

A truncated dopamine D-3-receptor-like mRNA, named D-3nf, predicts a p rotein that differs from the D-3-receptor only in the carboxyl terminu s. However, such a protein has lost the predicted membrane topology ty pically found for G protein-coupled receptors. Results presented here show that D-3nf mRNA arises from the D-3-encoded primary transcript vi a alternative splicing. This splicing, however, appears to involve cle avage of an unusual 3' splice site. Therefore, we tested the possibili ty that D-3nf mRNA results from a splicing error. If this were the cas e, D-3nf mRNA would be expected to be present in the cytoplasm only at very low amounts, and it would not be expected to be translated into protein. However, the relative abundance of cytoplasmic D-3/D-3nf mRNA in human cortical tissues was found to be similar. Furthermore, we ra ised polyclonal antisera against the predicted carboxyl-terminal pepti de sequence of D-3nf that reacts specifically with a protein expressed in stably D-3nf mRNA-expressing COS 7 cells. The use of this antiseru m also revealed the presence of a similar to 68 kDa D-3nf like immunor eactive protein in human brain, suggesting that the atypically process ed D-3nf mRNA is translated.