Transposable elements in sexual and ancient asexual taxa

Sexual reproduction allows deleterious transposable elements to proliferate in populations, whereas the loss of sex, by preventing their spread, has been predicted eventually to result in a population free of such elements [Hickey, D. A. (1982) Genetics 101, 519-531]. We tested this expectation by screening representatives of a majority of animal phyla for LINE-like and gypsy-like reverse transcriptases and mariner/Tc1-like transposases. All species tested positive for reverse transcriptases except rotifers of the class Bdelloidea, the largest eukaryotic taxon in which males, hermaphrodites, and meiosis are unknown and for which ancient asexuality is supported by molecular genetic evidence. Mariner-like transposases are distributed sporadically among species and are present in bdelloid rotifers. The remarkable lack of LINE-like and gypsy-like retrotransposons in bdelloids and their ubiquitous presence in other taxa support the view that eukaryotic retrotransposons are sexually transmitted nuclear parasites and that bdelloid rotifers evolved asexually.

Evidence for the evolution of bdelloid rotifers without sexual reproduction or genetic exchange

The Class Bdelloidea of the Phylum Rotifera is the largest metazoan taxon in which males, hermaphrodites, and meiosis are unknown. We conducted a molecular genetic test of this indication that bdelloid rotifers may have evolved without sexual reproduction or genetic exchange. The test is based on the expectation that after millions of years without these processes, genomes will no longer contain pairs of closely similar haplotypes and instead will contain highly divergent descendants of formerly allelic nucleotide sequences. We find that genomes of individual bdelloid rotifers, representing four different species, appear to lack pairs of closely similar sequences and contain representatives of two ancient lineages that began to diverge before the bdelloid radiation many millions of years ago when sexual reproduction and genetic exchange may have ceased.

On the mode of gene-dosage compensation in Drosophila

A procedure is described for determining the mode and magnitude of gene-dosage compensation of transformed genes. It involves measurement of the ratio of the activity of a gene inserted at X-linked sites to the activity of the same gene inserted at autosomal sites. Applying the procedure to the Drosophila pseudoobscura Hsp82 gene inserted at ectopic sites in D. melanogaster and taking gene activity as proportional to the amount of transcript per gene copy, we conclude that (1) in both adults and larvae the gene is not compensated at autosomal sites or at a site in beta-heterochromatin at the base of the X chromosome and is fully compensated at euchromatic X-chromosomal sites; (2) inappropriate normalization is responsible for a claim that the gene is compensated at autosomal sites; and (3) the observed compensation operates mainly or entirely by heightened activity of X-linked genes in males, rather than by reduced activity in females.

The Sverdlovsk anthrax outbreak of 1979

In April and May 1979, an unusual anthrax epidemic occurred in Sverdlovsk, Union of Soviet Socialist Republics. Soviet officials attributed it to consumption of contaminated meat. U.S. agencies attributed it to inhalation of spores accidentally released at a military microbiology facility in the city. Epidemiological data show that most victims worked or lived in a narrow zone extending from the military facility to the southern city limit. Farther south, livestock died of anthrax along the zone's extended axis. The zone paralleled the northerly wind that prevailed shortly before the outbreak. It is concluded that the escape of an aerosol of anthrax pathogen at the military facility caused the outbreak.

Production and cleavage of Drosophila hsp70 transcripts extending beyond the polyadenylation site

Transcription downstream of the polyadenylation site was studied in the Drosophila hsp70 gene, whose high level of transcription in response to temperature elevation facilitates detection of rare and possibly short-lived transcripts. Transcription downstream of the polyadenylation site was detected both in cultured cells and in intact animals. Even shortly after temperature elevation the extended nonpolyadenylated RNAs were rare relative to mature message, and their level continued to increase following temperature elevation even after the amount of mature message stopped increasing. The extended transcripts therefore are unlikely to be message precursors. Although continuous transcripts were detected extending as far as 2 kb downstream of the normal polyadenylation site, the predominant extended transcript was 0.45 kb long, apparently produced by cleavage of longer transcripts. Its amount relative to mature message increased with the duration and severity of heat-shock. As is the case in nonpolyadenylated histone mRNA, there is a potential stem-loop structure just upstream of the cleavage site. These data and other lines of evidence suggest that this extended transcript results from an alternative mode of stable 3'-end formation.

Dosage compensation of the Drosophila pseudoobscura Hsp82 gene and the Drosophila melanogaster Adh gene at ectopic sites in D. melanogaster

Measurements were made of the amounts of larval RNA transcribed from the autosomal Adh gene of Drosophila melanogaster and the X chromosomal Hsp82 gene of Drosophila pseudoobscura carried on the same P-element transposon inserted at various sites in the D. melanogaster genome. Both genes were fully compensated at sites in euchromatic regions of the X chromosome but neither was compensated at a site in the centric beta-heterochromatin of the X chromosome. No compensation of the D. pseudoobscura Hsp82 gene was found at any of 10 autosomal insertion sites tested. The compensation behavior of the transposed genes was, therefore, not determined by closely linked sequences but instead was determined in each case by their new chromosomal environment.

Drosophila retrotransposon promoter includes an essential sequence at the initiation site and requires a downstream sequence for full activity

We describe a 98-base-pair region (-38 to +60) in the long terminal repeat of the Drosophila gypsy retrotransposon that is sufficient for accurate normal-level transcription. We find that, unlike most RNA polymerase II (pol II) promoters, the gypsy promoter includes downstream sequences that are required for full activity. Also unlike most pol II promoters, the gypsy promoter, which lacks a TATA motif, was found to have an essential sequence at the transcription initiation site, mutation of which abolishes transcription. These three uncommon features of the gypsy promoter may be characteristic of a subset of pol II promoters, exemplified by certain retrotransposons and developmental genes of Drosophila and by Tdt, the mouse terminal deoxynucleotidyl-transferase (TdT) gene.

Alteration of hsp82 gene expression by the gypsy transposon and suppressor genes in Drosophila melanogaster

Several mutations in Drosophila result from insertion of the gypsy retrotransposon. Gypsy insertion mutagenesis and its modulation by allele-specific modifier genes were investigated by inserting gypsy or fragments of it into the intron of the Drosophila hsp82 heat shock gene. With gypsy in the parallel orientation, nearly all transcripts in transfected cells and transformed pupae were truncated in the 5' long terminal repeat (LTR). Truncation also occurred in or near the 3' LTR. The 5' LTR polyadenylation signal was strongly potentiated by a downstream 326-bp internal gypsy segment in either orientation. Anti-parallel gypsy reduced the amount of normal transcript to a much smaller extent, and a low level of truncation occurred within gypsy. No evidence was found for effects of the gypsy insertions on the hsp82 promoter. Mutations in the allelespecific modifier genes su(f) and su(w alpha) had effects on the amounts of readthrough transcripts consistent with their genetic behavior, whereas the effects of mutations in su(Hw) were only partly in accord with genetic expectations.

Genetic interactions of modifier genes and modifiable alleles in Drosophila melanogaster

We have examined the effects of mutations in the six allele-specific modifier genes su(Hw), e(we), su(f), su(s), su(wa), and su(pr) on the expression of 18 modifiable alleles, situated at 11 loci. Ten of the modifiable alleles are associated with insertions of the gypsy retrotransposon and the others include alleles associated with insertions of copia and 412. We tested or retested 90 of the 108 possible combinations and examined the expression of modifiable alleles in flies mutant for pairs of modifier genes in various heterozygous and homozygous configurations. Our principal findings are: (1) a screen of 40,000 mutagenized X chromosomes yielded three new mutations in known modifier genes, but revealed no new modifier genes; (2) the modification effects of different mutations in a given modifier gene were qualitatively similar; (3) each of the six modifiers suppressed some modifiable alleles, enhanced others, and had no noticeable effect on still others; (4) the modifier genes could be placed in four classes, according to their effects on the gypsy-insertion alleles; and (5) the effects of mutations in different modifier genes combined additively. Implications of these results for models of modifier gene action are discussed.

Periodic interactions of heat shock transcriptional elements

The activity of some genes is known to be a periodic function of the amount of DNA between the binding sites of its regulatory proteins. The period observed is close to 10.5 base pairs (bp), that is, one turn of the B form of the DNA helix. Such periodicity is also seen in the cooperative binding of phage lambda and lac repressors. These periodic phenomena have been attributed to a requirement for a unique rotational alignment in forming essential contacts between the bound proteins. Here we report a strong periodic dependence of the transcription of a cloned Drosophila melanogaster heat shock gene on the amount of DNA inserted between its two heat shock consensus elements. In addition, we find a similar periodicity for insertions just 3' to the proximal heat shock element. Consistent with the torsional flexibility of DNA, these periodic effects are seen for short insertions, up to approximately 80 bp, but not for much longer ones. We conclude that maximal transcription requires rotationally unique contacts between proteins bound to the two heat shock elements and also requires correct alignment of additional sites of DNA-protein binding downstream of the proximal element.

Interspecific nucleotide sequence comparisons used to identify regulatory and structural features of the Drosophila hsp82 gene

We have sequenced the hsp82 heat shock gene and 5'-flanking DNA of four species of Drosophila in order to identify conserved features of possible regulatory significance and to determine the nature and rate of evolutionary change in various domains of the gene. All conserved sequences identified in the 5' non-transcribed region of the hsp82 gene of melanogaster, simulans, pseudoobscura and virilis lie within 150 base-pairs of the RNA initiation site. These include a 34 base-pair imperfect but highly conserved dyad made up of three overlapping copies of the consensus heat shock regulatory sequence dyad made up of three overlapping copies of the consensus heat shock regulatory sequence C-T-N-G-A-A-N-N-T-T-C-N-A-G. Several other highly conserved features are also seen. In pseudoobscura only, the region from -21 to -133 is almost exactly repeated 698 base-pairs upstream. The upstream repeat retains all of the sequences common to the four species in the -21 to -133 interval except for the T-A-T-A motif. One possibility is that this upstream sequence is involved in dosage compensation of the hsp82 gene, which is pseudoobscura is on the X chromosome. In melanogaster, simulans and virilis there is an oppositely oriented, non-heat shock gene 0.6 to 0.8 kb (kb = 10(3) base-pairs) upstream from the hsp82 transcription initiation site. Comparisons of the hsp82 transcription unit from the distantly related species show little or no sequence conservation in the intron and non-translated exon I sequences. In contrast, the coding regions of these species are 90% homologous at the DNA level and 97 to 99% identical at the amino acid level. Half of the amino acid changes have occurred within a 15-amino acid region that lies within an unusually polar domain of hsp82. From the sequence comparisons, we estimate the rate of silent (synonymous) site substitution in Drosophila as 1 X 10(-8)/nucleotide site per year, similar to that for mammals.

Separate regulatory elements for the heat-inducible and ovarian expression of the Drosophila hsp26 gene

We have constructed and transformed into the D. melanogaster germ line a series of hsp26 deletion variants. We show that the region -728 to +14 contains all of the cis-acting sequences necessary for the developmental and heat-inducible transcription of hsp26. Sequences upstream of -341 are not required for heat-inducible expression but are required for ovarian expression. Conversely, sequences between -351 and -53 are unnecessary for ovarian expression but are needed for maximal heat-inducible expression. We conclude that most, or all, of the cis-acting regulatory sequences required for hsp26 gene expression during oogenesis are physically separable from those required for heat-inducible expression. These results suggest that different trans-acting factors bind at different regulatory sites in the 5'-flanking region of the gene, thus activating its transcription.

Inducible transcription and puffing in Drosophila melanogaster transformed with hsp70-phage lambda hybrid heat shock genes

A series of hsp70-phage lambda hybrid genes having various amounts of 5' flanking DNA was introduced into the germ line of Drosophila melanogaster by P-element-mediated transformation. Heat-induced transcription was normal in lines transformed with hsp70-lambda genes having 194 and 146 base pairs of DNA upstream from the mRNA initiation site. Lines transformed with genes having 70 base pairs of upstream DNA accumulated correctly initiated transcripts in response to heat shock, but the amount was somewhat reduced and minor amounts of incorrectly initiated transcripts were observed. No transcription, with or without heat shock, was seen in lines transformed with hsp70-lambda genes having only 52, 44, or 25 base pairs of upstream DNA. Heat shock induced polytene chromosome puffing at the site of integration in a line transformed with a gene having 194 base pairs of upstream DNA. The hsp70-lambda gene and a cotransformed Adh gene closely linked on the same integrating fragment were expressed independently, each apparently responding only to its own normal control signals.

Long terminal repeat nucleotide sequence and specific insertion of the gypsy transposon

We have determined the nucleotide sequences of the long terminal repeats of the transposable element gypsy from the cloned mutant alleles sc1, bx3, and bx34e. These mutations are suppressible by the suppressor of Hairy-wing, su(Hw). The long terminal repeats are 482 base pairs long and are highly conserved. In each case, gypsy is inserted into the sequence T-A-C-A-T-A and generates a duplication of the sequence T-A-C-A. This was verified by sequencing an empty site in the wild-type bx gene. Consideration of the sequence of the long terminal repeats and their surroundings limits the possible explanations for the mechanism of mutation by these gypsy insertions and for their suppression by su(Hw).

Effects of high levels of DNA adenine methylation on methyl-directed mismatch repair in Escherichia coli

Two methods were used in an attempt to increase the efficiency and strand selectivity of methyl-directed mismatch repair of bacteriophage lambda heteroduplexes in E. coli. Previous studies of such repair used lambda DNA that was only partially methylated as the source of methylated chains. Also, transfection was carried out in methylating strains. Either of these factors might have been responsible for the incompleteness of the strand selectivity observed previously. In the first approach to increasing strand selectivity, heteroduplexes were transfected into a host deficient in methylation, but no changes in repair frequencies were observed. In the second approach, heteroduplexes were prepared using DNA that had been highly methylated in vitro with purified DNA adenine methylase as the source of methylated chains. In heteroduplexes having a repairable cI/+ mismatch, strand selectivity was indeed enhanced. In heteroduplexes with one chain highly methylated and the complementary chain unmethylated, the frequency of repair on the unmethylated chain increased to nearly 100%. Heteroduplexes with both chains highly methylated were not repaired at a detectable frequency. Thus, chains highly methylated by DNA adenine methylase were refractory to mismatch repair by this system, regardless of the methylation of the complementary chain. These results support the hypothesis that methyl-directed mismatch repair acts to correct errors of replication, thus lowering the mutation rate.

Accumulation of a specific subset of D. melanogaster heat shock mRNAs in normal development without heat shock

During normal development in D. melanogaster, messenger RNAs for three of the seven heat shock proteins (hsp83, hsp28 and hsp26) accumulate in adult ovaries and are abundant in embryos until blastoderm. The three mRNAs appear to originate in nurse cells and subsequently pass, during stages 10-11, into the oocyte. Little if any of the four other heat shock mRNAs is present in unshocked ovaries or embryos at any time examined. Pre-blastoderm embryos fail to accumulate these heat shock mRNAs even if subjected to heat shock. The accumulation in normal oogenesis of mRNAs for only three of the seven heat shock proteins indicates the existence of differential, possibly multiple controls of heat shock gene expression, and suggests that heat shock proteins hsp83, hsp28 and hsp26 function in the oocyte or early embryo.

Drosophila melanogaster mutations suppressible by the suppressor of Hairy-wing are insertions of a 7.3-kilobase mobile element

Certain spontaneous mutations of Drosophila melanogaster are suppressed by su(Hw), the suppressor of Hairy-wing (3R-54.8). We find that mutations suppressible by su(Hw) result from insertions of a mobile element at the affected loci. The element, named gypsy, is approximately 7.3 kilobases long and includes 0.5-kilobase direct terminal repeats. It was first identified in DNA cloned from the bithorax chromosomal region of several Drosophila stocks carrying suppressible mutations of the bithorax complex. Cloned gypsy DNA was used as a probe to test for the association of gypsy with suppressible mutations at various other loci by hybridization in situ. Gypsy was found to be associated with 19 suppressible alleles at 10 different loci: yellow, Hairy-wing, scute, diminutive, cut, lozenge, forked, Beadex, hairy, and the bithorax complex. It was found with wild-type or nonsuppressible mutations at any of these loci. Gypsy DNA was also used as a probe to clone the element and adjacent unique DNA from the loci of some suppressible mutations. This confirmed the presence of the full-length element and also provided cloned DNA from the previously uncloned loci scute and cut. The suppressor of Hairy-wing is generally recessive and behaves as a null mutation. Thus, the disruption of normal gene function caused by the inserted gypsy element appears to require some product of the wild-type suppressor gene, su(Hw)+.

Integration, transcription, and control of a Drosophila heat shock gene in mouse cells

Mouse L cells were transformed with a cloned 3.6-kilobase (kb) segment of Drosophila melanogaster DNA carrying the 2.25-kb transcribed sequence for the Drosophila 70,000-dalton heat shock protein (hsp70) and 1.1 kb and 0.2 kb of 5' and 3' flanking DNA, respectively. Heat shock of one of three such transformed cell lines containing multiple copies of the intact Drosophila segment induced the abundant accumulation of transcripts of the Drosophila gene, with correct or nearly correct 5' and 3' termini. This provides evidence, in accord with earlier indications, that diverse eukaryotes, including vertebrates, have heat shock systems similar to that studied extensively in Drosophila. Our results suggest that the signals for heat shock transcription and the chromosomal sites with which they interact have been highly conserved in evolution and that the regulatory sequences controlling transcription of the gene for hsp70 lie within the 3.6-kb Drosophila segment.

Sequence homologies in the 5' regions of four Drosophila heat-shock genes

We report nucleotide sequences of the regions surrounding the 5' ends of the genes for Drosophila melanogaster heat-shock proteins hsp83, hsp68, and hsp26, located at chromosome positions 63BC, 95D, and 67B, respectively. As in other eukaryotic genes, the sequence T-A-T-A-A-A-A-T occurs about 30 nucleotides upstream from the sites of mRNA initiation. Three additional sequence homologies and a dyad symmetry were noted at approximately corresponding locations in the three genes and in the gene for another heat-shock protein, hsp70. We also found an intron near the 5' end of the hsp83 gene, with sequences at its boundaries typical of splice sites found in other organisms.

Four heat shock proteins of Drosophila melanogaster coded within a 12-kilobase region in chromosome subdivision 67B

Unique coding sequences for four heat shock proteins of Drosophila melanogaster, hsp 28, hsp 26, hsp 23, and hsp 22, are clustered in a 12-kilobase interval at chromosome subdivision 67B. The four genes are not transcribed in the same direction and each gives rise to a separate messenger RNA, with no indication of intervening sequences. Including the present results, the genes for all seven major heat shock proteins of D. melanogaster are now cloned are found to exhibit a variety of patterns of organization at the five loci they occupy.

Plasmid screening at high colony density

A procedure is described for screening bacterial colonies containing recombinant plasmids by nucleic acid hybridization at high density, i.e., at 100 000 colonies per 150 mm diameter plate. Small colonies are established on nitrocellulose filters from which they can be faithfully replicated to additional filters. Chloramphenicol amplification may be carried out in situ before screening. The filters may be kept frozen for long-term storage of colonies which may be further replicated after thawing.

Studies of cloned sequences from four Drosophila heat shock loci

DNA cloned from the D. melanogaster (Oregon R) heat shock loci at 63BC and 95D codes for the 83,000 and the 68,000 dalton heat shock proteins, respectively. Both coding sequences occur once per haploid genome. Sequences complementary to messenger RNA for the 70,000 dalton heat shock protein are represented five times, twice at 87A and three times at 87 C. The copies at 87A differ characteristically from those at 87C in an interval of a few hundred bp near the 5' end of the messenger sequence, and the corresponding two classes of hsp 70 messenger RNA are found on polysomes after heat shock. Within this differential region, there is about 15% divergence between messenger sequences cloned from the two loci, while in the rest of the messenger region examined the homology is much closer although still imperfect. Unexpectedly, considerable homology is found between the sequence for the 68,000 dalton heat shock protein at 95D and the sequences for the 70,000 dalton protein at 87A and 87C, and between these sequences and a site in 87D. Messenger RNA molecules of 2.4, 2.55 and 3.05 kb code for the 68,000, 70,000 and 83,000 dalton heat shock proteins and hybridize to apparently uninterrupted DNA sequences of 2.1, 2.25 and 2.6 kb, respectively.

Sequence organization and transcription at two heat shock loci in Drosophila

The heat shock loci of Drosophila melanogaster chromosome subdivisions 87A and 87C have been studied by using cloned DNA. Both sites contain a number of copies of a 2,4-kilobase (kb) region homologous to mRNA for the 70,000-dalton heat shock protein. In situ hybridization to chromosomal RNA shows that transcripts of this sequence accumulate at both sites after temperature elevation. At 87C there is a 1.5-kb repeated sequence homologous to another heat shock RNA. One cloned segment includes two to three tandem copies of this sequence located 0.8 kb from the beginning of a 2.4-kb message region. RNA complementary to the 1.5-kb repeat acccumulates at 87C after temperature elevation, but does not code for any known heat shock protein. In the sibling species D. simulans, there are sequences located and transcribed at 87A and 87C that are homologous to the melanogaster 2.4-kb message sequence. The 1.5-kb repeat, however, is absent from 87C in simulans and no heat shock RNA homologous to it can be detected.

Transcription at two heat shock loci in Drosophila

Transcription at two heat shock loci in Drosophila melanogaster, in subdivisions 87A and 57C, was investigated by hybridization in situ with 3H-labeled messenger, nuclear RNA and whole cell RNA from cells cultured at elevated temperature. What appears to be the same 9 x 10(5) dalton heat shock message hybridizes at both sites. At 87a, little additional hybridization is obtained with nuclear or whole cell RNA. In contrast, at 87C the saturation level of hybridization by nuclear and whole cell RNA is much higher than that obtained with the message alone. This evidence for extensive hybridization at 87C but not at 87A by RNA distinct from the message is confirmed by the finding that excess nonradioactive message competes away most of the hybridization by 3H-labeled nuclear and whole cell RNA at the latter locus but not at the former. The noncompetable RNA migrates on an electrophoretic gel as a heterogeneous population of molecules, extending to sizes both larger and smaller than the message. These and other observations lead to the conclusion that a 87A transcription includes little more than sequences complementary to the 9 x 10(5) dalton message, while at 87C, there are sequences complementary to the same message and extensive additional sequences complementary to other species of RNA.

Single burst study of rec- and red-mediated recombination in bacteriophage lambda

Single bursts from three-point crosses of bacteriophage lambda were analyzed for recombination of markers several thousand nucleotide pairs apart. Single recombination, mediated by the rec system of Escherichia coli, is usually reciprocal. Double recombinants are also significantly correlated in single bursts, although the correlation is weaker than for reciprocal singles. Reciprocity is not found in crosses mediated by the lambda red system. With respect to certain other paraments of recombination, the two systems appear to be alike. Double recombinants usually result from one event, not from two independent single recombinations, and their average clone size is about half that of single recombinants. The results are discussed in terms of current molecular models of recombination.

Repair tracts in mismatched DNA heteroduplexes

Heteroduplexes with mismatches at four sites were constructed from separated strands of lambda DNA and used to transfect Escherichia coli under recombinationless conditions. The output phages from 967 single cells in one experiment and 1016 in another were analyzed to determine the pattern of mismatch repair. A wide range of repair frequencies was found among the mismatches studied. Repair involving two or more close sites in the same heteroduplex occurs much more often on thesamestrandthanonopposite strands. Analysis of the pattern of repair suggeststhat repair tracts initiate at mismatches, propagate preferentially in the 5'leads to 3' direction, and extend an average distance of ca 3000 nucleotides.

Mismatch repair in heteroduplex DNA

DNA with base pair mismatches was prepared by annealing mixtures of genetically marked DNA from bacteriophage lambda. This heteroduplex DNA was used to transfect bacteria under conditions minimizing recombination. Genetic analysis of the progeny phages indicates that: (i) Mismatch repair occurs, usually giving rise to a DNA molecule with one chain with the genotype arising from repair and one parental chain. (ii) The frequency of repair of a given mismatch to wild type depends on the marker, ranging from 3 to 20%. (iii) Excision tracts may extend several hundred nucleotides but are usually shorter than about 2000 nucleotides. (iv) In Rec-mediated bacteriophage crosses, recombination of markers closer than about 10-3 nucleotide pairs frequently occurs by mismatch repair within heteroduplex DNA. (V) The average amount of heteroduplex DNA formed in a Rec-mediated recombination event is a few thousand nucleotide pairs.

Localization of RNA from heat-induced polysomes at puff sites in Drosophila melanogaster

Heat treatment of D. melanogaster tissue culture cells causes drastic changes in the pattern of protein synthesis and the size distribution of polysomes. Like the heat shock puffs on polytene chromosomes which appear while preexisting puffs regress, heat shock proteins appear on gels while the synthesis of preexisting proteins is sharply reduced, and heat-induced polysomes appear on gradients after preexisting polysomes have disappeared. Most of the poly(adenylic acid)-containing RNA isolated from high-temperature polysomes sediments in sucrose gradients and migrates in gels as a rather narrow band. This RNA is of sufficient size to code for one particular protein that is found to account for more than half of the total synthesis at high temperature. The RNA hybridizes in situ mainly at chromosome sub-division 87B, the site of the major heat shock puff.

DNA modification methylase activity of Escherichia coli restriction endonucleases K and P

The highly purified restriction endonucleases of E. coli K and coliphage P1 transfer methyl groups from S-adenosylmethionine to adenine residues of unmodified DNA. Incubation of unmodified DNA with endonucleases K or P and S-adenosylmethionine renders the DNA resistant to restriction. The enzymes, therefore, have both restriction endonuclease and modification methylase activities.

A T4-induced endonuclease which attacks T4 DNA

A DNA endonucleolytic activity that introduces single-stranded breaks into native T4 DNA is found in T4-infected E. coli. This endonuclease attacks other double-stranded, but not single-stranded, DNA. Experiments with ultraviolet-irradiated phages and amber mutants indicate that the enzyme is made beginning about five minutes after infection at 37 degrees C.

A specific complex between a restriction endonuclease and its DNA substrate

In the presence of Mg(++), ATP, and S-adenosylmethionine, the DNA restriction endonuclease R.K forms a specific complex with its DNA substrate. The complex can be detected by its retention on nitrocellulose membranes.