Sometimes after yum install automake we have :

Downloading Packages:
warning: rpmts_HdrFromFdno: Header V3 DSA signature: NOKEY, key ID db42a60e


Public key for autoconf-2.59-5.noarch.rpm is not installed

This errors occurs sometime with yum install the old GPG keys are obsolote, you have to update them :

rpm --import /etc/pki/rpm-gpg/RPM*