transcript targetting.

[FOF%FDACFSAN.bitnet at VM.CFSAN.FDA.GOV]

THis is in response to a posting by Derek.  My understanding of the current
understanding of protein targeting is that specificity is mediated entirely
by protein (rather than mRNA) sequences.  In other words, the localization of a
 protein is governed by the presence/absence of a signal sequence/mitochondrial
 localization/vacuolar/chloroplast/etc. and that there is a single biochemical
class of cytoplasmic ribosomes.  Am I wrong?  If I am wrong, what is the eviden
ce that suggests I am wrong?  Is there clear evidence that untranslated mRNA
sequences are actually involved in protein localization?  What is this evidence
?