Detection and abundance of mRNA and protein encoded by transposable element activator (Ac) in maize.

The 3.5 kb long mRNA of the maize transposable element Ac contains an open reading frame (ORFa) which encodes a polypeptide of 807 amino acids, the putative transposase of Ac. The Ac mRNA is a rare transcript: we now estimate the fraction of Ac mRNA in wx-m7::Ac seedlings to be 2-13 x 10(-5) of the polyA RNA. Assuming that maize cells contain similar amounts of polyA RNA as another monocot (0.16 pg/cell), this is equivalent to 1.5-10 transcripts in each cell. A protein with an apparent molecular weight of 112 kDa is detected, by five antisera directed against different segments of ORFa, exclusively in nuclear extracts from Ac-containing maize. This protein is most likely the full-length Ac ORFa protein. We estimate its concentration to be in the range of 3 x 10(-7) of the nuclear proteins, or about 1000 molecules per triploid endosperm cell containing one Ac element.

Analysis of sh-m6233, a mutation induced by the transposable element Ds in the sucrose synthase gene of Zea mays.

The unstable allele sh-m6233 caused by insertion of the transposable element Ds into the sucrose synthase gene of maize, was cloned. The mutation is caused by the insertion of an 4 kb DNA segment, consisting of two identical Ds elements of 2000 bp length, of which one is inserted into the center of the other in inverted orientation. This structure is, at the level of restriction mapping and partial DNA sequencing, identical to the double Ds element found in a larger insert in the mutant allele sh-m5933. 8 bp of host DNA are duplicated upon insertion. In a revertant, a 6-bp duplication is retained.

Studies on T4-head maturation. 2. Substrate specificity of gene-49-controlled endonuclease.

The substrate specificity of 49+-enzyme was investigated in vitro. The enzyme showed a marked preference for rapidly sedimenting T4 DNA (greater than 1000 S) when helix-destabilizing proteins from Escherichia coli or phage T4 were added to the reaction. Regular replicative T4 DNA (200-S DNA) or denatured T4 DNA was not cleaved by the enzyme in the presence of these proteins but if they were omitted from the reaction both DNAs become good substrates for the enzyme. 200-S DNA was cleaved at its natural sites of single strandedness which occur at one-genome intervals. Gaps in T4 DNA which were constructed by treatment of a nicked DNA with exonuclease III were also cleaved by 49+-enzyme in the absence of helix-destabilizing proteins. Single-stranded T4 DNA was extensively degraded and up to 50% of the material was found to be acid-soluble in a limit digest. The degradation products were predominantly oligonucleotides of random size. No preference for a 5'-terminal nucleotide was observed in material from a limit digest with M13 DNA. Double-stranded DNA was nicked upon exposure to 49+-enzyme and double-strand breakage finally occurred by an accumulation of single-strand interruptions. No acid-soluble material was produced from native T4 DNA. The introduction of nicks in native DNA did not improve its properties as a substrate for the enzyme. Double-stranded DNA was about 100-fold less sensitive to the enzyme than single-stranded DNA.