The role of chromosomal proteins HMG‐14 and HMG‐17 in the generation of transcriptionally active chromatin was studied in a Xenopus laevis egg extract which supports complementary DNA strand synthesis and chromatin assembly. Chromosomal proteins HMG‐14/HMG‐17 enhanced transcription from a chromatin template carrying a 5S rRNA gene, but not from a DNA template. The transcriptional potential of chromatin was enhanced only when these proteins were incorporated into the template during, but not after, chromatin assembly. HMG‐14 and HMG‐17 stimulate transcription by increasing the activity, and not the number, of transcribed templates. They unfold the chromatin template without affecting the nucleosomal repeat or decreasing the content of histone B4. We suggest that HMG‐14/HMG‐17 enhance transcription by inducing an extended conformation in the chromatin fiber, perhaps due to interactions with histone tails in nucleosomes. By disrupting the higher order chromatin structure HMG‐14/HMG‐17 increase the accessibility of target sequences to components of the transcriptional apparatus.

Stanniocalcin (STC) is an anti-hypercalcemic glycoprotein hormone previously identified in the corpuscles of Stannius in bony fish and recently in the human genome. This study undertook to express human STC in Chinese hamster ovary (CHO) cells and to determine its effects on calcium and phosphate absorption in swine and rat intestine. Unidirectional mucosal-to-serosal ( J m→s) and serosal-to-mucosal ( J s→m)45Ca and32P fluxes were measured in vitro in duodenal tissue in voltage-clamped Ussing chambers. Addition of STC (10–100 ng/ml) to the serosal surface of the duodenum resulted in a simultaneous increase in calcium J m→s and J s→mfluxes, with a subsequent reduction in net calcium absorption. This was coupled with an STC-stimulated increase in phosphate absorption. Intestinal conductance was increased at the highest dose of STC (100 ng/ml) in swine tissue. The addition of STC to the mucosal surface had no effect on calcium and phosphate fluxes. STC at doses of 10–1,000 ng/ml had no effect on short-circuit current in any region of the rat intestine. In conclusion, human recombinant STC decreases the absorption of calcium and stimulates the absorption of phosphate in both swine and rat duodenum. STC is a novel regulatory protein that regulates mammalian intestinal calcium and phosphate transport.

A cell‐free system from Xenopus eggs was used to study the role of chromosomal protein HMG‐17 in the generation of the chromatin structure of transcriptionally active genes. Addition of HMG‐17 protein to the extracts, which do not contain structural homologs of the HMG‐14/−17 protein family, indicates the protein is incorporated into the nascent template during replication, prior to completion of chromatin assembly. The protein binds to and stabilizes the structure of the nucleosomal core thereby improving the apparent periodicity of the nucleosomal spacing of nascent chromatin. Assembly of HMG‐17 into the nascent chromatin structure significantly increased the transcription potential of the 5S RNA gene and satellite I chromatin. Kinetic studies indicate that the increase in transcriptional potential is observed only when HMG‐17 is incorporated into nucleosomes during chromatin assembly.

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