The recA genes of Proteus vulgaris, Erwinia carotovora, Shigellaflexneri and Escherichia coli B/r have been isolated and introduced into Escherichia coli K-12. All the heterologous genes restore resistance to killing by UV irradiation and the mutagen 4-nitroquinoline-1-oxide in RecA-E. coli K-12 hosts. Recombination proficiency is also restored as measured by formation of Lac' recombinants from duplicated mutant lacZ genes and the ability to propagate phage A derivatives requiring host recombination functions for growth (Fec-). The cloned heterologous genes increase the spontaneous induction of prophage in lysogens of a recA strain. Addition of mitomycin C stimulates phage production in cells carrying the E. coli B/r and S. flexneri recA genes, but little or no stimulation is seen in cells carrying the E. carotovora and P. vulgaris recA genes. After treatment with nalidixic acid, the heterologous RecA proteins are synthesized at elevated levels, a result consistent with their regulation by the E. coli K-12 LexA repressor. Southern hybridization and preliminary restriction analysis indicate divergence among the coding sequences, but antibodies prepared against the E. coli K-12 RecA protein cross-react with the heterologous enzymes, indicating structural conservation among these proteins. * Corresponding author. chemical agents. These and other observations suggest that the recA gene product might be conserved in a wide variety of procaryotes and eucaryotes. Consistent with this view are (1) JC14604 F-lacMS286080II A. J. Clark (27) lacBKI dl(srl-recA) hsr C600 recA56 F-sri (TnlO) recA56 This lab DM1187A21 F-lexA(Def) This lab d121(srl-recA) sfi SK8710 C600 recA56(pMK710) This study SK9816 C600 recA56(pMK816) This study SK2184 C600 recA56(pMK184) This study SK8815 C600 recA56(pMK815) This study SK9100 C600 recA56(pBR322) This study SK9700 C600 recA56(Yrpl2) This study SK7710 JC14604(pMK710) This study SK8816 JC14604(pMK816) This study SK1184 JC14604(pMK184) This study SK7815 JC14604(pMK815) This study SK7840 JC14604(Yrpl2) This study SK7860 JC14604(pBR322) This study SK3500 C600 recA56(pBR-E. This study coli recA+)
In the majority of pregnancies involving a Down's syndrome (DS) fetus, the level of alpha-fetoprotein (AFP) measured in maternal serum and amniotic fluid is reduced to about 70 per cent of the level attained in normal pregnancies. Causes of this decrease may include the production of an altered AFP molecule with modified turnover or transport properties, or a reduction in the level of AFP synthesis. We examined hepatic AFP mRNA transcripts and compared AFP polypeptide isoforms in liver tissue samples obtained from a group of DS and normal abortuses. No differences was detected in the structure of the AFP mRNA transcript or in the charge or mass of AFP polypeptides in the two sample groups. However, the hepatic AFP level, expressed as microgram AFP/mg protein, was significantly lower in a group of 28 DS cases relative to a group of 47 normal controls (p = 0.04). This difference in hepatic AFP concentration did not appear to be the result of a general reduction in the level of total protein or total RNA production. The greatest difference between the AFP levels of the DS and normal groups was observed in the earliest samples examined (i.e., at 17-19 weeks of age) where the median AFP levels differed by about 20 per cent.
We assayed maternal serum samples from 134 black and 268 white women from 16 to 18 weeks of gestation for intact human chorionic gonadotropin (hCG), and unconjugated oestriol (uE3). Serum from women with high (> or = 2.5 MOMs) or low (risk for Down syndrome > or = 1/365) maternal serum alpha-fetoprotein (MSAFP) levels were excluded. After correcting for maternal weight, we found that median hCG levels were 16 per cent higher in black women but uE3 levels were not significantly different. These results confirm three other studies for hCG and one study for uE3. Corrections are recommended for both maternal serum hCG and AFP before calculating the risk for Down syndrome in black women.
Ten Nicotiana species were assayed for the proportion of DNA that is complementary to ribosomal RNA. This proportion varies from 0.27 to 0.9 percent, with tetraploid species having lower values than the diploid species. The tetraploid species have about twice as much DNA per cell as do diploid species. Thus, the absolute number of genes for ribosomal RNA varies less than the proportion of complementary DNA. Further, the number of genes for the RNA in 80S ribosomes varies less among species than does that for the RNA in 70S ribosomes. The data indicate that loss of DNA complementary to ribosomal RNA is associated with tetraploidy in the genus Nicotiana.
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