The mycobacterial guaB1 gene encodes a guanosine 5'-monophosphate reductase with a cystathionine-β-synthase domain.

Mycobacteria express enzymes from both the de novo and purine-salvage pathways. However, the regulation of these processes and the roles of individual metabolic enzymes have not been sufficiently detailed. Both Mycobacterium tuberculosis (Mtb) and Mycobacterium smegmatis (Msm) possess three guaB genes, but information is only available on guaB2, which encodes an essential inosine 5'-monophosphate dehydrogenase (IMPDH) involved in de novo purine biosynthesis.

Publisher Correction: Anti-CRISPR proteins encoded by archaeal lytic viruses inhibit subtype I-D immunity.

In the original version of this Article, molecular weight markers in Figs 1c, 2c,d and 4d were displaced during the production process, so that they were not correctly aligned with the corresponding bands. In addition, in Fig. 4c, molecular masses given for three different elution volumes were displaced so that they appeared to the left of the correct positions.

Anti-CRISPR proteins encoded by archaeal lytic viruses inhibit subtype I-D immunity.

Viruses employ a range of strategies to counteract the prokaryotic adaptive immune system, clustered regularly interspaced short palindromic repeats and CRISPR-associated proteins (CRISPR-Cas), including mutational escape and physical blocking of enzymatic function using anti-CRISPR proteins (Acrs). Acrs have been found in many bacteriophages but so far not in archaeal viruses, despite the near ubiquity of CRISPR-Cas systems in archaea. Here, we report the functional and structural characterization of two archaeal Acrs from the lytic rudiviruses, SIRV2 and SIRV3.