Circular dichroism studies of the interaction of a limited hydrolysate of T4 gene 32 protein with T4 DNA and poly[d(A-T)].poly[d(A-T)]

gp32 I is a protein with a molecular weight of 27 000. It is obtained by limited hydrolysis of T4 gene 32 coded protein, which is one of the DNA melting proteins. gp32 I itself appears to be also a melting protein. It denatures poly[d(A-T)].poly[d(A-T)] and T4 DNA at temperatures far (50-60 degrees C) below their regular melting temperatures. Under similar conditions gp32 I will denature poly[d(A-T).poly[d(A-T)] at temperatures approximately 12 degrees C lower than those measured for the intact gp32 denaturation. For T4 DNA gp32 shows no melting behavior while gp32 I shows considerable denaturation (i.e., hyperchromicity) even at 1 degree C. In this paper the denaturation of poly[d(A-T)].poly[d(A-T)] and T4 DNA by gp32 I is studied by means of circular dichroism. It appears that gp32 I forms a complex with poly[d(A-T)]. The conformation of the polynucleotide in the complex is equal to that of one strand of the double-stranded polymer in 6 M LiCl. In the gp32 I DNA complex formed upon denaturation of T4 DNA, the single-stranded DNA molecule has the same conformation as one strand of the double-strand T4 DNA molecule in the C-DNA conformation.

Effects of lead inhalation exposures alone and in combination with carbon monoxide in nonpregnant and pregnant rats and fetuses. II. Effects on delta-aminolevulinic acid dehydratase activity, hematocrit and body weight

Pregnant and nonpregnant rats were exposed for 21 days to an aerosol containing 1, 3 and 10 mg lead/m3 air and to a combination of 3 mg Pb/m3 and 500 ppm carbon monoxide (CO). Pregnant and nonpregnant rats exposed to uncontaminated air served as controls. The activity of the fetal delta-aminolevulinic acid dehydratase (ALA-D) was less inhibited by lead than the maternal activity. Furthermore, the degree of inhibition was highly reduced in the fetuses by additional CO-inhalation, whereas in adult animals the depression of the ALA-D was accentuated by additional CO-inhalation in accordance with epidemiological data. Therefore, it is concluded that the mode of plumbic inhibition of the ALA-D activity differs in fetuses from that in adults. Furthermore, the adaptation to the inhibition of the ALA-D by de novo synthesis of this enzyme was less in fetuses than in adult rats. The high lead aerosol concentration reduced hematocrit and body weight of the fetuses, but it did not influence these parameters in adult rats, thus pointing to a higher lead-sensitivity of the fetal than the adult organism. A stronger inhibition of maternal ALA-D activity than of the activity of nonpregnant animals possibly indicates a higher susceptibility to lead in pregnancy.