ISSN:
1617-4623
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary The opt-r2 marker is integrated into the discriminating pneumococcal strain C13 as a LE marker, but after passage through the strain SIII-1 it was integrated as an HE marker at the higher concentrations of the transforming DNA. As the transforming DNA was diluted the integrating efficiencies reverted to the expected LE values. The high content of DNA derived from strain SIII-1 in the transforming DNA was causing the hex system in the recipient strain C13 be ‘swamped’ at the higher DNA concentrations, thus allowing the opt-r2 marker to escape the hex action. A similar state was obtained by adding to an homologous transforming system an excess of strain SIII-1 DNA which again ‘swamped’ the hex system and gave an HE integration for the opt-r2 marker. It was shown that even homologus DNA at the higher concentrations was capable of causing ‘swamping’ of the hex system, and hence the integration efficiencies should always be measured at low concentrations of the transforming DNA. Furthermore, all the markers utilised with the possible exception of the amiA-r110 marker, showed some sensitivity to the hex system, supporting the suggestion that all markers show differing degrees of low efficiency, i.e., the HE markers should really be regarded as less LE than the LE markers, whilst VHE markers are probably the only markers not subject to hex action. It is suggested that the differing degrees of low efficiency represent differing affinities of a hex system enzyme for its substrate, i.e. the lower the efficiency the greater the affinity. The degree of affinity may be determined by a recognition site associated with the marker, each site being a certain sequence of base pairs. Introduction of a marker into a different hex + recipient strain (strain R6) resulted in a new integration efficiency and in a reduced level of marker rescue by the ‘swamping’ SIII-1 DNA. It is suggested that not all the discriminating strains possess identical hex systems reacting to the same set of recognition sites.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00271210
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