VISUALIZATION OF POLY(A)-BINDING PROTEIN COMPLEX-FORMATION WITH POLY(A) RNA USING ATOMIC-FORCE MICROSCOPY

Poly(A)-binding protein (PABP) is an RNA-binding protein that binds sp ecifically to the poly(A) tail of messenger RNAs in eukaryotes. The PA BP/poly(A) tail complex has been implicated as being important in prom oting the efficient initiation of translation as well as in maintainin g the integrity of the mRNA. PABP binds poly(A) cooperatively with a p acking density of one PABP molecule per 25 adenosine residues. We have investigated the complexes formed between purified PABP and poly(A) R NA using atomic force microscopy (AFM). PABP alone was observed to be primarily in a monomer form with a height of 1.0 +/- 0.2 nm. Following binding to poly(A), PABP appeared to be present in variable size comp lexes that bound lengthwise along the RNA. This size of the PABP/poly( A) complex appeared to be maximal, suggesting that PARR binding to pol y(A) may be self-limiting. Poly(A) RNA alone appeared to contain a kno b-like structure that largely disappeared once PABP was bound. The use of AFM has therefore provided potential new insights into the complex es formed by this RNA-binding protein. (C) 1997 Academic Press.