substitute last space with char

I would like to replace the last occurrence of a space in a line with a ';'.

I know I can use:
g_ " goto last non-blank char in line
F " find the preceeding ' '
r; " replace with ';'

How would this be done with :substitute ?

--
--
You received this message from the "vim_use" maillist.
Do not top-post! Type your reply below the text you are replying to.
For more information, visit http://www.vim.org/maillist.php

---
You received this message because you are subscribed to the Google Groups "vim_use" group.
To unsubscribe from this group and stop receiving emails from it, send an email to vim_use+unsubscribe@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.