NUCLEAR DOT ANTIGENS MAY SPECIFY TRANSCRIPTIONAL DOMAINS IN THE NUCLEUS

A bank of 892 human autoimmune serum samples was screened by indirect immunofluorescence on human tissue culture HT-29 cells. Seven serum sa mples that stain 4 to 10 bright dots in cell lines of several differen t mammals, including humans, monkeys, rats, and pigs, were identified. Immunofluorescence experiments indicate that these antigens, called n uclear dot (ND) antigens, are distinct from splicing complexes, kineto chores, and other known nuclear structures. An ND antigen recognized b y these sera was cloned by immunoscreening a human lambdagt11 expressi on library. Analysis of seven cDNA clones for the ND antigen indicates that several mRNAs exist, perhaps derived through alternative splicin g mechanisms. One major form of the message has an open reading frame of 1,440 bp capable of encoding a 53,000-M(r) protein. Treatment of ce lls with detergent, salt, or RNase A fails to remove the ND antigen fr om the nucleus. However, incubation with DNase I obliterates ND staini ng, indicating that the ND protein directly or indirectly associates w ith nuclear DNA. Fusion of the ND protein to a LexA DNA binding domain activates transcription in Saccharomyces cerevisiae. A 75-amino-acid domain that activates transcription in both yeast and primate cells ha s been identified. We suggest that ND antigens may participate in the activation of transcription of specific regions of the genome.