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Two mannose-binding lectins, Allium sativum agglutinin (ASA) I (25 kDa) and ASAIII (48 kDa), from garlic bulbs have been purified by affinity chromatography followed by gel filtration. The subunit structures of these lectins are different, but they display similar sugar specificities. Both ASAI and ASAIII are made up of 12.5-and 11.5-kDa subunits. In addition, a complex (136 kDa) comprising a polypeptide chain of 54 ؎ 4 kDa and the subunits of ASAI and ASAIII elutes earlier than these lectins on gel filtration. The 54-kDa subunit is proven to be alliinase, which is known to form a complex with garlic lectins. Constituent subunits of ASAI and ASAIII exhibit the same sequence at their amino termini. ASAI and ASAIII recognize monosaccharides in mannosyl configuration. The potencies of the ligands for ASAs increase in the following order: mannobiose (Man␣1-3Man) < mannotriose (Man␣1-6Man␣1-3Man) Ϸ mannopentaose < < Man 9 -oligosaccharide. The addition of two GlcNAc residues at the reducing end of mannotriose or mannopentaose enhances their potencies significantly, whereas substitution of both ␣1-3-and ␣1-6-mannosyl residues of mannotriose with GlcNAc at the nonreducing end increases their activity only marginally. The best manno-oligosaccharide ligand is Man 9 GlcNAc 2 Asn, which bears several ␣1-2-linked mannose residues. Interaction with glycoproteins suggests that these lectins recognize internal mannose as well as bind to the core pentasaccharide of N-linked glycans even when it is sialylated. The strongest inhibitors are the high mannose-containing glycoproteins, which carry larger glycan chains. Indeed, invertase, which contains 85% of its mannose residues in species larger than Man 20 GlcNAc, exhibited the highest binding affinity. No other mannose-or mannose/glucose-binding lectin has been shown to display such a specificity.The majority of the well characterized plant lectins have been isolated from the seeds of dicotyledonous species. But lectins of non-seed origin from other species are also emerging as promising tools chiefly because of two reasons: (i) a good number of them might contain novel sugar-binding sites; and (ii) they can provide valuable information regarding the biological roles of plant lectins, which to a large extent still remain elusive. In the recent past, there have been several reports of non-seed lectins from monocotyledonous families (1-3), especially Amaryllidaceae. The most remarkable property of these lectins is that they show strict specificity for mannose (2, 4, 5), unlike other mannose/glucose-binding plant lectins. Hence, they are being used extensively as affinity ligands for the purification of glycoproteins, viz. IgM, ␣ 2 -macroglobulin, haptoglobin, and ␤-lipoprotein (3, 6).Van Damme et al. (3) examined a number of species (including Allium sativum) from the family Alliaceae (which is taxonomically close to the family Amaryllidaceae) and found them to accumulate mannose-binding lectins. They observed that lectins from both families share many common properties like their ...

DNA Topoisomerase I (TopoI) in eubacteria is the principle DNA relaxase, belonging to Type 1A group. The enzyme from Mycobacterium smegmatis is essential for cell survival and distinct from other eubacteria in having several unusual characteristics. To understand genome-wide TopoI engagements in vivo, functional sites were mapped by employing a poisonous variant of the enzyme and a newly discovered inhibitor, both of which arrest the enzyme activity after the first transestrification reaction, thereby leading to the accumulation of protein-DNA covalent complexes. The cleavage sites are subsets of TopoI binding sites, implying that TopoI recruitment does not necessarily lead to DNA cleavage in vivo. The cleavage protection conferred by nucleoid associated proteins in vitro suggest a similar possibility in vivo. Co-localization of binding and cleavage sites of the enzyme on transcription units, implying that both TopoI recruitment and function are associated with active transcription. Attenuation of the cleavage upon Rifampicin treatment confirms the close connection between transcription and TopoI action. Notably, TopoI is inactive upstream of the Transcription start site (TSS) and activated following transcription initiation. The binding of TopoI at the Ter region, and the DNA cleavage at the Ter indicates TopoI involvement in chromosome segregation, substantiated by its catenation and decatenation activities.

The genotoxic effects of the herbicide dicamba have been studied by measuring 1) the unwinding rate of liver DNA from intraperitoneally (i.p.) treated rats (fluorimetric assay); 2) DNA repair as unscheduled DNA synthesis (UDS) induced in cultured human peripheral blood lymphocytes (HPBL); and 3) sister chromatid exchanges (SCE) in HPBL. Results show that dicamba is capable of inducing DNA damage since it significantly increases the unwinding rate of rat liver DNA in vivo and also induces UDS in HPBL in vitro in the presence of exogenous metabolic activation (S-9 mix). Furthermore, dicamba causes a very slight increase in SCE frequency in HPBL in vitro.