Bacillus subtilis Smc condenses chromosomes in a heterologous cell system, which is down-regulated by ScpAB.

We show that expression of BsSmc leads to strong chromosome compaction, while expression of ScpAB does not show any effect. Chromosome compaction by Smc was also found for mutant versions lacking ATP binding or ability for head engagement, and was counteracted by concomitant expression of ScpAB. Our findings show that the SMC complex can act as autonomous condensation system in a heterologous bacterial host system, for which neither ATP binding nor ATP hydrolysis are required. Our investigation suggests that the negative effect on compaction activity of Smc exerted by ScpAB in vivo does not involve an effect on ATPase activity, but more likely a stabilization of the engagement of head domains, which in turn may affect ATPase activity.