G-quadruplexes are noncanonical structures formed by G-rich DNA and RNA 
sequences that fold into a four-stranded conformation. Experimental studies and 
computational predictions show that RNA G-quadruplexes are present in 
transcripts associated with telomeres, in noncoding sequences of primary 
transcripts and within mature transcripts. RNA G-quadruplexes at these specific 
locations play important roles in key cellular functions, including telomere 
homeostasis and gene expression. Indeed, RNA G-quadruplexes appear as important 
regulators of pre-mRNA processing (splicing and polyadenylation), RNA turnover, 
mRNA targeting and translation. The regulatory mechanisms controlled by RNA 
G-quadruplexes involve the binding of protein factors that modulate G-quadruplex 
conformation and/or serve as a bridge to recruit additional protein regulators. 
In this review, we summarize the current knowledge on the role of G-quadruplexes 
in RNA biology with particular emphasis on the molecular mechanisms underlying 
their specific function in RNA metabolism occurring in physiological or 
pathological conditions.