7 RNA, Lipids, and Membranes

Abstract

Could there be a deep cellular connection between the RNA World and the world of bilayer membranes formed from amphipathic lipids? Although the answer may seem to be “no,” a connection is surprisingly plausible. In fact, a superficial, more polar zone exists in bilayer membranes, and it makes up about half of the depth of the bilayer (Wiener and White 1992). Within these shallow polar fields are many ionic head groups, polar glycerol, and fatty acid carbonyls with which RNA can associate, as well as solvating water. If required, RNA can also have stabilizing, shape-sensitive interactions with nonpolar aliphatics (reviewed below), such as the fatty acids in a biological membrane’s core. Thus, an RNA is easily envisioned associated with, or floating in, a membrane.

This kind of reasoning sent us on the search for membrane activities in pure RNAs. The most complex expression of this search is presently a membrane RNA that serves in vitro as a passive, specific membrane transporter for the amino acid tryptophan (Janas et al. 2004). In this chapter, we undertake a short review of the known connections between RNAs and lipids, including those in membranes. Our purpose is serious, but partly playful, too: Below are some potential connections between worlds. One can have some grave fun playing with the possibilities for further interactions.

HYDROPHOBIC SITES ON RNA
We begin with a notion introduced just above; somewhat surprisingly, RNA can fold to reveal hydrophobic patches of specific size and shape. In fact, our metaphorical interface between...