Does RSA Private key always contain the Public key, or is it just .NET?

public static string Sign(string data, string privateAndPublicKey)
    {
        byte[] dataBytes = Encoding.UTF8.GetBytes(data);
        RSACryptoServiceProvider provider = CreateProviderFromKey(privateAndPublicKey);
        byte[] signatureBytes = provider.SignData(dataBytes, "SHA1");
        return Convert.ToBase64String(signatureBytes);
    }

    public static bool Verify(string data, string signature, string publicKey)
    {
        byte[] dataBytes = Encoding.UTF8.GetBytes(data);
        byte[] signatureBytes = Convert.FromBase64String(signature);
        RSACryptoServiceProvider provider = CreateProviderFromKey(publicKey);
        return provider.VerifyData(dataBytes, "SHA1", signatureBytes);
    }

    private static RSACryptoServiceProvider CreateProviderFromKey(string key)
    {
        RSACryptoServiceProvider provider = new RSACryptoServiceProvider();
        provider.FromXmlString(key);
        return provider;
    }