Paul M. Doty, professor of Chemistry, has recently succeeded in separating and recombining the two strands of bases which comprise the helical structure of DNA.

"Our chief problem," he stated yesterday, "has been to unite two strands from different strains of bacteria." By extracting DNA from two different strains and providing proper conditions for recombination, Doty produced bacteria showing both mutations. This proved that single strands from each of the two mutants combined to form the DNA of the new strain.

Test for Bacteria

Doty pointed out that similar experimental procedures can be used to determine whether the base sequence in different strains of bacteria is similar. "If a large amount of hybridization occurs between two different strains," he said, "there is similarity in their DNA base sequences."

The reason is that when two strands form a helix, each of the four kinds of bases in a strand must face a particular kind of base, its complement, in the opposite strand. Hybridization occurs only where strands of DNA are complementary and suggests similarity in base sequence.

To determine the extent of hybridization, the DNA strand of one strain of bacteria is made heavier by introducing heavy nitrogen. If this chain "mates" with a chain of normal weight to form a hybrid, the weight of the resulting DNA will lie midway between the normal and heavy DNA.

Now in his fourteenth year at Harvard, Doty has made other significant contributions in the area of protein synthesis. In addition to his work with DNA, he is currently examining the role of RNA, the other nucleic acid, which is believed to contribute to protein synthesis by controlling the unwinding of the genetic information carried in DNA.