Bacterial chromosome (nucleoid) conformation dictates faithful regulation of gene transcription. The conformation is condition-dependent and is guided by several nucleoid-associated proteins (NAPs) and at least one nucleoid-associated noncoding RNA, naRNA4. Here we investigated the molecular mechanism of how naRNA4 and the major NAP, HU, acting together organize the chromosome structure by establishing multiple DNA–DNA contacts (DNA condensation). We demonstrate that naRNA4 uniquely acts by forming complexes that may not involve long stretches of DNA–RNA hybrid. Also, uncommonly, HU, a chromosome-associated protein that is essential in the DNA–RNA interactions, is not present in the final complex. Thus, HU plays a catalytic (chaperone) role in the naRNA4-mediated DNA condensation process.
SMC complexes in bacterial chromosome condensation and segregation
