Molecular Studies of Chromosomal Protein H-NS"

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Molecular architecture of chromosomes remains one of the major mysteries of modern genetics. In spite of impressive advances made in learning the nucleotide sequence of chromosomes, the mechanisms of packing functional DNA into the small space available is unsolved. One organizing mechanism is supercoiling. DNA is found supercoiled in all organisms to about the same extent. Another puzzle is the fact that only a fraction of the genetic information is actively used at any instant. Learning how DNA is organized in both active and inactive regions of chromosomes is known as the domain problem. Bacteriophage MU is one of the most useful tools for studying chromosome structure. Mu is a transposon that randomly inserts itself into bacterial chromosomes and creates its own supercoiled domain using host enzymes and proteins. Further, through novel Mu genetics, it was discovered that one of the most abundant chromosomal proteins in E. coli, H-NS, supercoils DNA. DNA supercoiled by H-NS is inactive for transcription. Thus, H-NS is a prime candidate for organizing inactive supercoiled domains. Experiments are designed to probe the structure of H-NS interactions with Mu DNA using genetic approaches as well as chemical and enzymatic probes and electron microscopy.