Q:

putting 1 input into 2 mysql databases

I am wondering if it is possible to put the content of 1 input field of a register form into 2 different tables (ie email address into login and user_account tables) - Here is the question updated.

A:

simple stuff:
$conn1 = "database1"; //your first database connection
$conn2 = "database"; //your second database connection

$email =  mysqli_real_escape_string($conn1, $_POST['email']);    

$query = "INSERT INTO table (email) VALUES ($email)";

$run1 = mysqli_query($conn1 , $query);
$run2 = mysqli_query($conn2 , $query);

EDIT:
after reading the comments, its not 2 database's you are connecting to, its just one, using multiple tables. So:
$conn = //database connection

$email = $_POST['email'];

$query = "INSERT INTO table (email) VALUES ($email)";
$query2 = "INSERT INTO table2 (email) VALUES ($email);

$run = mysqli_query($conn , $query);
$run = mysqli_query($conn , $query2);

