4. It is known that construction teams A and B each have several workers. If team A lends 90 workers to team B, then the total number of workers in team B will be twice that of team A; if team B lends a certain number of workers to team A, then the total number of workers in team A will be 6 times that of team B. Team A originally had at least $\qquad$ workers.
4. 153.

Let team A originally have $a$ workers, team B originally have $b$ workers, and team B lend $c$ workers to team A.
From the problem, we have
$$
\begin{array}{l}
2(a-90)=b+90, \\
a+c=6(b-c).
\end{array}
$$

From equation (1), we get $b=2a-270$.
Substituting equation (3) into equation (2), we get
$$
c=\frac{11a-1620}{7}=a-232+\frac{4(a+1)}{7}.
$$

Since $c \geqslant 1$, thus, $a \geqslant 148$.
By $7 \mid 4(a+1)$, and $(4,7)=1$, then $7 \mid (a+1)$.
Therefore, the minimum value of $a$ is 153.