Question: Among the pairs of genes that are both located in the nucleus, what is the highest expression correlation score?
SQL: SELECT T2.Expression_Corr FROM Genes AS T1 INNER JOIN Interactions AS T2 ON T1.GeneID = T2.GeneID1 INNER JOIN Genes AS T3 ON T3.GeneID = T2.GeneID2 WHERE T1.Localization = 'nucleus' AND T3.Localization = 'nucleus' ORDER BY T2.Expression_Corr DESC LIMIT 1