[BioC] plot, drawing character string as ticks, not indizes

[Dipl.-Ing. Johannes Rainer]

hi,
is it possible in R to use character strings to be written as x axis 
ticks in a plot? for example i have a vector of values and i want to 
plot them, is it possible that for the x axis ticks not the index of 
the value in the vector is used, but for example an "a" ("b" and so on) 
is written?

thanks, jo