Part of the processive rRNA transcription and antitermination complex (rrnTAC). The complex forms an RNA-chaperone ring around the RNA exit tunnel of RNA polymerase (RNAP). It supports rapid transcription and antitermination of rRNA operons, cotranscriptional rRNA folding, and annealing of distal rRNA regions to allow correct ribosome biogenesis. This subunit may play a central role in organizing the structure (PubMed:32871103). Involved in 30S ribosomal subunit biogenesis; thought to be required for loop formation between NusB/NusE (rpsJ, ribosomal protein S10) bound to boxA upstream of the rRNA operons and the elongating RNAP complex. This would promote correct co-transcriptional folding of rRNA. Plays a role in transcription antitermination in a plasmid context in vivo (PubMed:26980831). Required for rrn transcription antitermination; required for integration of NusB/NusE into the antitermination complex (PubMed:31020314). The Nus factor complex (NusA, NusB, NusE (rpsJ), NusG and SuhB) represses expression of suhB and possibly other genes via boxA; the Nus complex prevents or promotes Rho-mediated transcription termination depending on gene context (PubMed:29229908). Involved in post-transcriptional control of gene expression (Probable). Enzymatic activity is not required for complementation of the cold-sensitive phenotype of the dnaB121 mutation (PubMed:10747806) (Probable). Has D,L-inositol-1-monophosphatase and beta-glycerophosphatase activity, has less to no activity against a number of other substrates (PubMed:8002619). 2.5-fold more active on 1D-inositol-1-monophosphate than L-inositol-1-monophosphate (1D-myo-inositol 3-phosphate). Specific activity increases significantly upon heating. Only beta-glycerophosphate and adenosine 2'-monophosphate are alternative substrates (PubMed:10747806). Required for growth at low temperatures (PubMed:2138605, PubMed:6389495, PubMed:1847383, PubMed:8002619, PubMed:8589060, PubMed:17652087, PubMed:26980831). Identified as a suppressor (ssyA3) of a temperature-sensitive, protein export missense mutation of secY (secY24), allows growth at 42 but not 30 degrees Celsius (PubMed:6389495). Identified as a suppressor (suhB2) of an rpoH missense mutation (rpoH15), allowing growth at 37 and 40 but not 25, 30 or 34 degrees Celsius, increases expression of RpoH (PubMed:2138605). Identified as a suppressor of a dnaB helicase missense mutation (dnaB121), restores growth at 42 but not 30 degrees Celsius (PubMed:1847383). In both suhB2 and ssyA3 there is an insertion in the 5' region of the gene which prevents SuhB protein expression (PubMed:8002619, PubMed:8589060). Missense mutant suhB10 is suppressed by mutations in RNase III (rnc), showing genetic interaction between them (PubMed:8589060). Deletion of suhB is suppressed by mutations in RNase III, by a mutation in nusA or deletion of nusB, indicating that in the absence of SuhB the Nus complex inhibits growth (PubMed:26980831). a myo-inositol phosphate + H2O = myo-inositol + phosphate 1D-myo-inositol 1-phosphate + H2O = myo-inositol + phosphate 1D-myo-inositol 3-phosphate + H2O = myo-inositol + phosphate Partial activity is seen with Co(2+), Ni(2+), Mn(2+), Zn(2+) and Fe(2+); in the presence of Mg(2+) these cations inhibit. Inhibited by Li(+) (PubMed:8002619, PubMed:10747806) (Probable). Li(+) binds to Asp-84, Asp-87 and Asp-212 (PubMed:22384802). Optimum pH is 7.8. Optimum temperature is 80 degrees Celsius, 90% of activity remains after heating at 70 degrees Celsius for 5 minutes. Monomer (PubMed:10747806, PubMed:31127279). A monomer-dimer equilibrium (PubMed:17652087). Homodimer (PubMed:31020314, PubMed:32871103). The rRNA transcription and antitermination complex (rrnTAC) consists of RNA polymerase (RNAP), NusA, NusB, NusE (rpsJ), NusG, SubB, ribosomal protein S4, DNA and precursor rRNA; S4 is more flexible than other subunits (PubMed:31127279, PubMed:31020314, PubMed:32871103). Binds to RNAP, which decreases IMPase activity against 1D-myo-inositol 1-phosphate (PubMed:17652087) (Probable). Association with rRNA gene-transcribing RNAP is dependent on NusB (PubMed:26980831, PubMed:29229908). Interacts with AR2 domain of NusA; crystallizes as a 2:1 SuhB:NusA heterotrimer (PubMed:31020314, PubMed:31127279). Transcription is autoregulated (PubMed:8831954). Repressed by the Nus factor complex (NusA, NusB, NusE (rpsJ), NusG and SuhB) (PubMed:29229908). Conditionally lethal, cells are unable to grow at 30 degrees Celsius and less, grow poorly at 37 degrees Celsius, but do grow at 42 degrees Celsius. E.coli makes very low amounts of myo-inositol-containing phospholipids, so the catalytic necessity for this enzyme is low. Belongs to the inositol monophosphatase superfamily.