Differential breakdown of phylogenetically diverse ribosomal RNA's inserted via liposomes into mammalian cells

Differential behavior of liposome-introduced specific RNAs in living Drosophila cells

We have developed a protocol for efficiently introducing macromolecules into Drosophila tissue culture cells using liposomes. By carefully adjusting the fusion parameters, conditions have been established to routinely encapsulate 15-30% of the starting material into liposomes and to introduce 20-30% of the liposome-encapsulated material into the cells during a 30-minute fusion period. Essentially, all of the cells receive material from the liposomes and 10(9) cells can be fused at once. The fusion does not have any measureable effect on cell viability as assayed by trypan blue exclusion, growth rate, and cell morphology. We have utilized this technique to introduce radioactive RNAs into nonradioactive cells, thus enabling the behavior of the introduced RNAs to be followed unambiguously. Liposome-introduced small nuclear RNAs (snRNAs) are stable in the cell for at least 25 hours (approximately two cell generations), with 80% of the radioactivity remaining trichloroacetic acid (TCA) precipitable and the gel electrophoresis pattern remaining essentially unchanged. This is in contrast to liposome-introduced cytoplasmic RNAs, which are only 20% TCA precipitable after the first hour. In the cell, the introduced snRNAs attain a 10-35-fold higher concentration in the nucleus than the cytoplasm. Nuclear accumulation is not seen with Drosophila tRNA or 5S RNA, both of which attain the same nuclear as cytoplasmic RNA concentration.

Liposomes with polyribonucleotides as model of precellular systems

A study of the encapsulation of poly(U) and poly(C) within liposomes made from dipalmitoylphosphatidyl choline (DPPC), from egg yolk phosphatidyl choline (PC), and from PC with cholesterol (CHOL) was made. The liposomes were prepared under anoxic conditions following the reverse-phase evaporation method. Determinations showed that 36 to 70% of the available lipids form liposomes and 2 to 5% of the polyribonucleotides can be entrapped by liposomes. The encapsulation of polyribonucleotides has also been measured in the presence of urea, cyanamide and Zn++, condensing agents in prebiotic polymerization reactions. DPPC and PC:CHOL liposomes were formed in the presence of 1.0 M urea, although no PC liposomes were formed. The three types of liposomes were readily formed at 0.01 M urea, but in no case an enhancement of encapsulation efficiency of poly(U) was observed due to the presence of urea. Similar results were obtained with cyanamide. An enhanced encapsulation of poly(U) by the three types of liposomes was observed when Zn++ was in the range of 0.001 to 0.01 M. Poly(U) encapsulation was 15 to 25 times higher when liposomes were prepared from DPPC at 0.01 M Zn++. Similar results were obtained with poly(C). The advantages of DPPC-polyribonucleotide liposomes as precellular systems are discussed.