expression

/Dear all,///
/I am very thankful, if you could tell what is the right way to write:

mtext(paste(expression("R"^2),round(marco2[1,i],digits=3),"   N? of proteins:",marco3[i]),side=4,cex=.6)

in this case the output is:

"R"^2

I tried also in this way:

mtext(paste(expression(paste("R"^2)),round(marco2[1,i],digits=3),"   N? of proteins:",marco3[i]),side=4,cex=.6)

the output is:

paste("R"^2)

Thank you in advance
Marco
/