Beschreibung:
The nucleic acid metabolism of young leaves (Nicotiana rustica, Pisum sativum) was investigated by 32P-labelling in short-time experiments. The nucleic acids were extracted quantitatively with buffer, containing SDS, and fractionated on the MAK column. Several rapidly labelled RNA fractions were found in the region of sRNS, DNA and rRNA. We have characterized two rapidly labelled fractions more detailed. The first one is a high molecular AU-RNA, which is eluted from the MAK column after the rRNA. The second one is a low molecular fraction in the region of the sRNA. The AU-RNA has the following properties: 1) It is rapidly labelled in pulse experiments. 2) the halfe-life of the AU-RNA in chase experiments is 4 hours at its maximum, showing faster degradation compared to the other fractions. 3) The 32P-incorporation is quantitatively inhibited by actinomycin D. 4) The base composition resembles DNA base composition (high AU and low GC content) . 5) AU-RNS appears as a heterogeneous fraction in the sucrose gradient, and sediments similar to rRNA. 6) AU-RNA occurs in all particle fractions of the homogenates. The low molecular, rapidly labelled RNA shows the following properties: 1) The radioactive peak does not correspond with 4 S or 5 S RNA peaks. 2) This RNA is metabolically stable, the radioactivity decreases very slowly in chase-experiments. 3) The 32P-incorporation is less inhibited by actinomycin D than the other RNA fractions. 4) The base composition is not similar to DNA base composition. A high content of labelled CTP in this RNA fraction may indicate the rapid 32P-incorporation by exchange of the terminal CpCpA group of tRNA. The possible messenger function of the AU-RNA is discussed.