This is a receiver domain (REC) commonly found in the same gene-neighbourhood of its cognate HK. Together they comprise a Two-Component System (TCS). There is a high degree of specificity among REC and DHp domains in a cognate pair. This domain is related to the Response_reg (pfam00072) domain. We found that pfam19191 and this domain show high degree of linkage in the same gene-neighbourhoods across several bacterial lineages. This implies that they comprise a TCS.