Structural domains comprising this superfamily share the structure of the all beta-stranded N-terminal domain of CarD from Mycobacterium tuberculosis (Mtb), an essential protein thought to be involved in stringent response through down-regulation of rRNA and ribosomal protein genes. CarD interacts with the beta-subunit of RNAP through its N-terminal domain with this interaction being vital for Mtb's survival during the persistent infection state. The structural fold of the CarD N-terminal domain is conserved in RNAP interacting proteins, such as TRCF.

CarD is DNA binding protein but the N-terminal domain is not involved in this process and mutation studies have revealed that the C-terminal domain is the DNA interaction domain.