Mary Ball


Many new restriction-modification (R-M) system which are closely linked to serB and allelic to the hsdSB system of S. typimurium occur in different Salmonella serotypes. In PI transduction studies with these systems, recombinants were isolated which fell into one of three classes with reference to their specific restriction phenotype. Recombinants that restricted like the donor, recombinants that restricted like the recipient and recombinants that had lost the ability to restrict. This latter group having lost the recipient SB restriction without gaining the specific donor restriction and here called "zero recombinants,” were of special interest and were investigated.

Zero recombinants were selected from among serB+ recombinants derived from transductions using phage PI, to E. coll/S. typhimurium LT2 hybrids 4662 (SBH+) and 4617 (SA+SB+). Backcrosses of these recombinants to 4662 and 4617 were also done. The modification phenotype of all recombinants was determined.

Three different phenotypes of zero recombinants were isolated in the transduction with S. eastbourne as donor: r-SBm-SBr-SEAm-SEA, r-SBm+SBr-SEAm-SEA, and r-SBm-SBr-SEAm+SEA. Since the SB and SEA R-M systems behaved as true alleles, the simplest explanation of the origin of these recombinant types was as the result of crossovers within the s and r genes of the two R-M systems. It is possible that the observation that zero recombinants were isolated more frequently when the co-transduction frequency of the complete R-M system was low (less than 5%) might be related to the fact that the R-M system would be close to the end of the transduced piece of DNA. Recent experiments have indicated that genetic recombination is initiated at the end of single-stranded pieces of DNA, (Hollman, Wiegand, Hoessli, and Radding, 1975). This could help to explain the high frequency of transduction of the "zero" phenotype.

LLU Discipline





Graduate School

First Advisor

Leonard R. Bullas

Second Advisor

Yuk Lin Ho

Third Advisor

Barry L. Taylor

Degree Name

Master of Science (MS)

Degree Level


Year Degree Awarded


Date (Title Page)




Library of Congress/MESH Subject Headings

Salmonella DNA; Recombinant



Page Count

iv; 35

Digital Format


Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.


Loma Linda University Electronic Theses and Dissertations

Collection Website


Loma Linda University. Del E. Webb Memorial Library. University Archives