Required for the formation of a threonylcarbamoyl group on adenosine at position 37 (t(6)A37) in tRNAs that read codons beginning with adenine. Is probably involved in the transfer of the threonylcarbamoyl moiety of threonylcarbamoyl-AMP (TC-AMP) to the N6 group of A37, together with TsaD and TsaE. TsaB seems to play an indirect role in the t(6)A biosynthesis pathway, possibly in regulating the core enzymatic function of TsaD. In fact, can act as a protease that specifically degrades TsaD in vitro; therefore TsaB may post-translationally regulate cellular pools of TsaD via proteolytic degradation. Does not show sialoglycoprotease activity against glycophorin A. Homodimer. Interacts with TsaD and TsaE in a mutually exclusive manner; TsaD is the preferred partner. Also interacts with TsaC. Appears essential for growth, since no null mutants can be obtained. Conditional depletion of this gene leads to enlarged cells, which display highly condensed nucleoids. The TsaB depletion phenotype is suppressed by overexpressing the response regulator RstA. TsaBCDE are necessary and sufficient for tRNA(NNU) t(6)A37 threonylcarbamoyladenosine modification in vitro in E.coli. Belongs to the KAE1 / TsaD family. TsaB subfamily. The well-known t(6)A modification appears to be a hydrolyzed artifact of natural cyclic t(6)A (ct(6)A) that occurs during the preparation and handling of tRNA in E.coli and many other species (PubMed:23242255). In these species, the t(6)A modification is processed further by dehydration into ct(6)A, a reaction catalyzed by TcdA.