We demonstrate that four different proteins from calf thymus are able to restore splicing in the same splicing-deficient extract using several different pre-mRNA substrates. These proteins are members of a conserved family of proteins recognized by a monoclonal antibody that binds to active sites of RNA polymerase II transcription. We purified this family of nuclear phosphoproteins to apparent homogeneity by two salt precipitations. The family, called SR proteins for their serine-and arginine-rich carboxy-terminal domains, consists of at least five different proteins with molecular masses of 20, 30, 40, 55, and 75 kD. Microsequencing revealed that they are related but not identical. In four of the family members a repeated protein sequence that encompasses an RNA recognition motif was observed. We discuss the potential role of this highly conserved, functionally related set of proteins in pre-mRNA splicing.

Mammals normally maintain their core body temperature (CBT) despite changes in environmental temperature. Exceptions to this norm include suspended animation-like states such as hibernation, torpor, and estivation. These states are all characterized by marked decreases in metabolic rate, followed by a loss of homeothermic control in which the animal's CBT approaches that of the environment. We report that hydrogen sulfide can induce a suspended animation-like state in a nonhibernating species, the house mouse (Mus musculus). This state is readily reversible and does not appear to harm the animal. This suggests the possibility of inducing suspended animation-like states for medical applications.

Alternative splicing of precursor messenger RNAs (pre-mRNAs) is a common mechanism of regulating gene expression. SR proteins are a family of pre-mRNA splicing factors that are structurally related and evolutionarily conserved. Any member of the SR family can complement a splicing-deficient extract that lacks the entire family of SR proteins. Here it is demonstrated that particular SR proteins have distinct functions in alternative pre-mRNA splicing in vitro. In addition, SR proteins are differentially expressed in a variety of tissues. These results suggest a fundamental role for SR proteins in the regulation of alternative splicing.

Abstract. An antibody was identified previously that recognizes sites of polymerase II transcription on lampbrush chromosomes, puffs on polytene chromosomes, and many small granules in the nucleoplasm of all cells tested . This antibody binds a conserved family of phosphorylated polypeptides in vertebrate and invertebrate cells . We developed a method for purifying these proteins that involves differential solubility in MgC12. We N ASCENT transcripts are bound by proteins, concomitant with synthesis by polymerase II . This was demonstrated in observations of ribonuclease treated amphibian lampbrush chromosomes (Gall and Callan, 1962) where it is possible to see nascent protein-bound transcripts by light microscopy, and was later confirmed by a number of studies in other systems (Malcolm and Sommerville, 1974;Lamb and Daneholt, 1979). Electron microscopic studies of transcription units using spreading techniques developed by Miller and colleagues confirmed this observation (Miller and Bakken, 1972).Because of their role in the elaboration ofgenetic information, there has been a major effort to identify transcriptbinding proteins. To date, two sets have been identified : hnRNP and snRNP proteins. The hnRNP proteins, which number at least 24, have been defined by biochemical cofractionation with radiolabeled hnRNA (Samarina et al., 1966;Beyer et al ., 1977) and more recently by immunochemical analysis (Pifiol-Roma et al., 1988) . Several genes encoding hnRNP proteins have been cloned and at least one protein has been shown to interact directly with RNA in vitro (Merrill et al., 1988) . Twelve snRNP proteins were identified by co-immunoprecipitation with snRNAs using an antibody that recognized a common epitope found on these proteins (Lerner and Steitz, 1979).We show here that a mAb 104 (mAb104), described as binding to lateral loops on amphibian lampbrush chromosomes (Roth et al., 1990) and to puffs on Drosophila polytene chromosomes (unpublished observation) binds a previously undescribed conserved family of nuclear phosphoproteins . Antigens recognized by mAbl04 do not coprecipitate with anti-hnRNP antibodies (Roth et al., 1990). We have cloned a gene that encodes a mAb104 immunoreactive protein from Drosophila melanogaster The encoded protein shares sequence homology with proteins involved in pre-mRNA splic-© The Rockefeller University Press, 0021-9525/91/11/587/10 $2 .00 The Journal of Cell Biology, Volume 115, Number 3, November 1991587-596 isolated a Drosophila cDNA encoding one of the proteins using information obtained from microsequencing . In vivo expression studies show that this protein is concentrated on sites of polymerase II transcription and that it is highly phosphorylated . The protein shares a high degree of homology with proteins involved in alternative splicing of pre-mRNA suggesting the possibility that this protein plays a role in pre-mRNA splicing .ing. We show that heterogeneously-sized RNA-but not snRNÁs-coprecipitate using mAb104 . Based on these experiments as well as in vivo expressio...