DEPOSITION OF CHROMOSOMAL PROTEIN HMG-17 DURING REPLICATION AFFECTS THE NUCLEOSOMAL LADDER AND TRANSCRIPTIONAL POTENTIAL OF NASCENT CHROMATIN

A cell-free system from Xenopus eggs was used to study the role of chr omosomal protein HMG-17 in the generation of the chromatin structure o f transcriptionally active genes. Addition of HMG-17 protein to the ex tracts, which do not contain structural homologs of the HMG-14/-17 pro tein family, indicates the protein is incorporated into the nascent te mplate during replication, prior to completion of chromatin assembly. The protein binds to and stabilizes the structure of the nucleosomal c ore thereby improving the apparent periodicity of the nucleosomal spac ing of nascent chromatin. Assembly of HMG-17 into the nascent chromati n 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.