This article is from the alt.security.keydist FAQ, by Michael Bauser firstname.lastname@example.org with numerous contributions by others.
Whatever PKE software you're using must be able to extract your public key
to a '7-bit', 'flat ascii', or 'plaintext' file. (Most PKE programs now
export keys in text format by default.) Once you've extracted your key,
just start an article to alt.security.keydist, cut-and-paste the keyfile
into your article, and post it.
Your subject line should state what software you're posting a key for,
and the e-mail address the key is for. I also recommend redirecting
followups to e-mail with a "Followup-To: poster" header, because
alt.security.keydist really isn't a discussion group.
You should repost your public key whenever it changes (i.e., you change
your e-mail address, add a certification, or revoke the key). Given the
ephemeral nature of netnews articles, periodically reposting unchanged keys
is acceptable. Users who expect to repost keys often should consider
adding "Expires:" and/or "Supersedes:" headers to their posts. The
documentation for your newsreading software should explain these headers.
MIME-educated PGP-users (and GPG-users) may want to use "Content-Type:
application/pgp-keys" for posting public keys. (This will make it easier
for many PGP users to import your key, but it may prevent Google Groups
from archiving the post containing the key.) See RFC 3156 at
http://www.ietf.org/rfc/rfc3156.txt for a description of the PGP media
By the way, don't clear-sign the message containing your public key! That
just makes it harder for people to add your key to their keyrings (Think
about it: How do people verify the signature if they don't yet have the key
on their keyring?) and does not verify the integrity of your key.