使用pycrypto,如何导入RSA公钥并使用它来加密字符串？

RSA公钥:

PUBKEY = 'MIGfMA0GCSqGSIb3DQEBA3UAA4GNADCBiQKBgQC35eMaYoJXEoJt5HxarHkzDBEMU3qIWE0HSQ77CwP/8UbX07W2XKwngUyY4k6Hl2M/n9TOZMZsiBzer/fqV + QNPN1m9M94eUm2gQgwkoRj5battRCaNJK/23GGpCsTQatJN8PZBhJBb2Vlsvw5lFrSdMT1R7vaz + 2EeNR/FitFXwIDAQAB'

如何导入并使用它来加密字符串？

我尝试了以下代码,但RSA.construct()引发了异常(TypeError:必须是long,而不是str).

from Crypto.PublicKey import RSA
from Crypto.Util import asn1
from base64 import b64decode

keyDER = b64decode(pubkey)
seq = asn1.DerSequence()
seq.decode(keyDER)
keyPub = RSA.construct((seq[0], seq[1]))
print keyPub.encrypt('mysecret', 32)

谢谢.