If there is only one Kohen present in the synagogue, and as the congregation begins the Torah reading he is still praying Pesukeh De’zimra, Shema, or the Berachot before or after Shema, may be go to the Torah to recite the Berachot? Would his recitation of the Berachot constitute a Hefsek (unlawful interruption), and thus be forbidden, or do we allow him to interrupt his prayer to receive the first Aliya to the Torah?
Hacham Ovadia Yosef (listen to audio recording for precise citation) rules that the Halacha in this case depends on which part of the prayer service the Kohen is currently reciting. If he is reciting Shema or the Berachot before of after Shema (meaning, from the Beracha of "Yoser Or" on), then he may not recite the Berachot over the Torah reading. In such a case, then, the congregation should not call the Kohen for the first Aliya, and should call a Yisrael in his place. (When no Kohen is present in the synagogue, a Yisrael, rather than a Levi, is called for the first Aliya.) However, if the Kohen is still reciting Pesukeh De’zimra, then he may be called to the Torah and recite the Berachot. He should also read along with the Ba’al Keri’a (reader). This is the ruling of the Hid"a (Rav Haim Yosef David Azulai, 1724-1806), in his work Kesher Godal (11:23). However, the Kohen may not speak or recite anything besides the Berachot and the Torah reading, such as a "Mi She’berach" for a pledge or for ill patients, or the Hashkaba prayer for the soul of a deceased person. Since these recitations do not relate to the actual Torah reading, they would constitute an unlawful interruption in the middle of Pesukeh De’zimra.
Summary: If the only Kohen in the synagogue is in the middle of Pesukeh De’zimra when the congregation begins the Torah reading, he should be called to the Torah, recite the Berachot, and read along with the reader. He may not speak or recite anything else. If the only Kohen is in the middle of Shema or the Berachot before or after Shema, he should not be called to the Torah, and a Yisrael should be called in his place.
