In Streptomyces spp. the principle sigma factor (aka SigA or HrdB) is required to transcribe housekeeping genes but they show using cryoEM and bioIT that the hrdB gene is transcribed by RNA polymerase containing an ECF sigma factor. Weird bacteria just got weirder

https://academic.oup.com/nar/article/53/8/gkaf339/8118975