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 samples that stain 4 to 10 bright dots in cell lines of several different mammals, including humans, monkeys, rats, and pigs, were identified. Immunofluorescence experiments indicate that these antigens, called nuclear dot (ND) antigens, are distinct from splicing complexes, kinetochores, and other known nuclear structures. An ND antigen recognized by these sera was cloned by immunoscreening a human lambdagt11 expression library. Analysis of seven cDNA clones for the ND antigen indicates that several mRNAs exist, perhaps derived through alternative splicing 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 cells with detergent, salt, or RNase A fails to remove the ND antigen from the nucleus. However, incubation with DNase I obliterates ND staining, indicating that the ND protein directly or indirectly associates with 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 has been identified. We suggest that ND antigens may participate in the activation of transcription of specific regions of the genome.