SQL string mutiple databases

I have mySQL installed.

On this server I have 3 database each with some tables.

1st database PERSONS contains a tables of persons (like name, password, email,…),
the two other databases contain the tables used to make the project. One for HRM and another for BILLING. So i have a project HRM and a project BILLING

So when opening project HRM i want to use data from the 1st database (PERSONS);
When using the project BILLING i want use the same data from database PERSONS.

Now i have to use 2 versions of the database PERSONS. Changing data twice when necessary.

Is this possible?