J. Biol. Chem., Vol. 261, Issue 19, 8617-8623, 07, 1986
Initial steps in Haemophilus influenzae transformation. Donor DNA binding in the com10 mutant
R Barouki and HO Smith
The com10 mutant of Haemophilus influenzae binds donor DNA reversibly, but
is deficient in uptake. The DNA binding has all the characteristics of
interaction with a protein receptor; it is saturable, reversible, and
specific. However, binding specificity is 6-fold weaker in com10 than is
uptake specificity in wild-type. The binding of small (120 base pairs) and
large (14,400 base pairs) DNA molecules were compared. For small molecules,
binding data fitted a straight line by Scatchard analysis (Bmax = 4.8 DNA
molecules/cell, Kd = 0.5 X 10(-9) M). In contrast, for large DNA molecules,
the Scatchard plot was not linear. A high affinity binding (Kd = 0.4 X
10(-12) M) and a lower affinity binding (Kd = 1.2 X 10(-11) M) were found
with a total number of 3 molecules bound per cell. In wild-type cells, 3.2
large molecules were taken up per cell, whereas up to 40 small 120-base
pair DNA fragments were taken up per cell. Uptake of small DNA molecules
followed a Michaelis-Menten function with a Km of 0.5 X 10(-9) M and a
maximal initial velocity of 1.5 molecules/cell/min at room temperature. For
large DNA molecules, maximal initial velocity was approximately 2
molecules/cell/min at room temperature. The analysis of the binding and
uptake data suggest to us that a receptor or a receptor complex is
responsible for the uptake of either a single large DNA molecule or,
successively, a number of small DNA molecules.