LlaGI was eluted with TMD plus 15 mM NaCl at 0

LlaGI was eluted with TMD plus 15 mM NaCl at 0.4 ml/min and monitored by measuring the absorbance at 280 nm. is usually a self-contained molecular motor that translocates DNA loops], we CE-224535 demonstrate that this communication is usually via 1-dimensional DNA loop translocation. On the basis of this data and that in the third accompanying manuscript [Smithet al. (2009) An Mrr-family nuclease motif in the single polypeptide restrictionmodification enzyme LlaGI], we propose that LlaGI is the prototype of a new sub-classification of Restriction-Modification enzymes, named Type I SP (for Single Polypeptide). == INTRODUCTION == LlaGI is usually a restrictionmodification (RM) enzyme isolated fromLactococcus lactisssp. cremoris W10 (1,2). It is encoded around the epigenetic element pEW104 and comprises the fusion of four putative protein domains (Physique 1A and B): an mrr-family nuclease (3,4); a Superfamily 2 (SF2) helicase (1; a -type adenine methyltransferase (MTase) (1); and a target recognition domain name (TRD) (1). Comparing the LlaGI primary amino acid sequences to the bacterial and archaeal sequences currently listed in the REBASE database (2) identifies 69 additional single polypeptide, helicase-containing RM enzymes (Table 1). Of these, two distinct groupings were noted on the basis of characteristic Walker A box sequences in their helicase domains: those with a GTGKT sequence which includes LlaGI (56 members) and those with an RFGKT sequence (14 members). Studies ofLactococcusbacteriophage CE-224535 infection show that LlaGI has efficient RM activity, producing at least a thousand-fold decrease CE-224535 in infectivity (1). However, details of the reaction mechanism of LlaGI, or any of the related enzymes, are not known. Whilst helicase-nuclease domain name fusions are also found in the ATP-dependent Type I and Type III RM enzymes (5,6), and nuclease-MTase domain name fusions are common to many sub-classes of Type II RM enzymes (79), the fusion of all three elements is unique to LlaGI and related enzymes. Thus LlaGI can be considered the prototype of a new sub-type of RM enzymes. On the basis of similarities in amino acid motifs and domain name organisation, Madsen and Josephsen (1) suggested that LlaGI is usually a variant of the Type I RM enzymes. Here, and in the accompanying papers (10,11), we provide an in-depth biochemical analysis of thein vitroenzymatic activities of LlaGI. On the basis of FKBP4 this data we discuss below the relationship of LlaGI to other RM enzymes of Types I, II and III, and suggest a suitable familial classification that is consistent with both domain name organisation and function. == Physique 1. == The LlaGI RM enzyme. (A) The SacI-NsiI region of pEW104 identified previously as sufficient forin vivoRM activity (1). The approximate locations of the putative promoter (P) and terminator (T) of the operon are indicated. (B) ThellagiRMgene product is usually a single polypeptide, multi-domain protein (1). Protein domain name boundaries were estimated using secondary structure prediction and alignment with LlaBIII (not shown). Target Recognition Domain name (TRD). (C) Recognition sequence of LlaGI. The adenine residue that is methylated is usually indicated by a circle. The arrowhead defines the directionality of the site according to cleavage (Physique 4) and translocation assays (10). The top strand sequence (i.e. that starting with CT) is usually quoted throughout. == Table 1. == LlaGI-like sequences identified from REBASE (2) Two distinct subgroups were observed with distinct sequences at helicase Motif I (the Walker A box). Note that some of these sequences have N-terminal deletions and/or mutations that may result in an inactive nuclease. == MATERIALS AND METHODS == == DNA == All oligonucleotides were supplied by MWG biotech (Germany). Plasmid pOne is usually pUC19 (12), and is re-named here for clarity. pZero was derived from pOne by QuikChange mutagenesis (Stratagene, La Jolla, CA) using primers 5-CCCGGCAACAATTAATAGATTGGATGGAGGCGGATAAAGTTGC-3 and 5-GCAACTTTATCCGCCTCCATCCAATCTATTAATTGTTGCCGGG-3 (where the LlaGI sequence is usually highlighted in strong and the mutated base pair underlined). The library of two-site plasmids (Physique 3) was generated by directional cloning of duplex oligonucleotides into the XbaI/HindIII fragment of plasmid pOne. One strand of each duplex oligonucleotide is usually shown inFigure 3B (white background). Where the sites are in direct repeat (where the top strand sequences inFigure 3are on the same DNA strand), the plasmids are named pHT forhead-to-tail. Where the sites are in indirect repeat, the plasmids are named pHH forhead-to-head (note that these DNA have sites in both head-to-head and tail-to-tail orientation). The sequence of Site is usually denoted by a numeric suffix (114), Site being constant (Physique 3B). Linear DNA CE-224535 substrates for the site identification experiments were produced by PCR using Pfu polymerase as directed by the.