How to define a new font inserting command in AucTeX?

[Gerald Wildgruber]

Can anyone help me with the definition of a new font command in AucTeX; I
would like to make 

C-c C-f C-g

insert the string

\textgreek{}

in analogy to the other font commands (like `C-c C-f C-e' for `\emph{}'),
with text between point an mark being placed inbetween the brackets.

How can I achieve this?

Thanks for your help,

Gerald.