Biochimica et Biophysica Acta 910 (1987) 21-26 21 Elsevier BBA 91743 Effects of DNA gyrase inhibitors in a polyamine-auxotrophic strain of Escherichia coil Vilma G. Duschak and Sara H. Goldemberg Instituto de Inoestigaciones Bioquimicas "Fundacion Campomar' and CONICET, Buenos Aires (Argentina) (Received 11 May 1987) Key words: DNA gyrase; DNA synthesis; Growth inhibition; Antibiotic; Nalidixic acid; Polyamine; (E. coli); (Polyamine-auxotrophic mutant) The polyamine content of the Escherichia coli polyamineiauxotrophic strain BGA 8 seemed to influence the effects of nalidixic acid, an antibiotic acting on subunit A of DNA gyrase. The growth rate was more affected under conditions of putrescine depletion and the inhibition could be partially relieved if the polycation was added back to the culture. DNA synthesis was likewise more sensitive to nalidixic acid in re,,pon~c. I'~ oked b) the anlibiotic, sho~ed a different persistence according, to the pre,,ence or absence .f pol,~amim'~ x,,~ ~d~iocin. actinla on subuni! B of ~.~ rasc, also promoted a differential effect dependinl~ on the pol.~amine ctmlent, hut in this case putresci.c-supplementcd cells ~erc more sensifi~e, fhc described findinl~s ~ll~e~t a role of pol)amines in all the reactions carried ou! h~ ~ rase. perhap,, due to lift' infh~em'c of the pol)catiom, on the slate of DNA a~l~re~ati41n. ! ntroduction I)NA supercoiling in baclcri',d cells, fundamcn- la] for genc expression 'and chromosollle repli- cation, is introduced and maintained b,, topoi~- omerasellor l)N~gyrasc[1 3]. This enzvme is a tetramer composed of two A subunits ( 31, 105 0fl01 and two B subunits (.~/, 05 000). coded for by txvo separate genes, grr,4 and gYr B respectively. Each subunit is specifically inhibited by some antibio- tics. Nalidixic acid and oxolinic acid affect sub- unit A. which is responsible for the processes involving the breakage and reunion activities of the enzyme (supercoiling. relaxation, catenalion :lnd decalenalion): counlernl\'cin A t ,~tnd no\(-~- ('nrrcspondencc It (;oldcmbcrg. In,liluto de [nvesligachme, Bioquimlca~. '" Fundaci,m (amp~mlar'" .\nlonin Machadn 1 ~ l (14(]q~ BtIOl~o- \ire,, Crgenmla hiocill block subunit B. which participate,, m AI P hvdroi\~i~ and cncr~v tr;,n~duction activities ~q gyrase ~upero~liitlg. \|]):~,*.' c;tlci;,~lion and dc- catenationt [1 3]. Several effcci~ of polyamines on lopol~o- merases have been described. Spermidinc at ph~- ological concentrations stimulates supercoilin~ b\ gyrase [4], and it is required for catenation and decatenation [5,6]. The polycation also ha~ an inhibitory effect on the relaxing activities of topoisomerases 1 and III, and on gyrase at high concentrations [7.81. It is important to mention that ionic strength is a significant factor of inter- action which may modify polyamine effects [6,,~J Since spermidine seems to modulate the activ- ity of DNA topoisomerases. Morris and Lnckshon 19] suggested that polyanline starvation in Escherichia coli should result in decreased super coiling of intracellular DNA. When the,, analysed the degree of ~upercoiling of a plasmid purified b~